Chrysler Full-Size Trucks 1967-1988 Repair Guide

Carburetor

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TROUBLESHOOTING



The best way to diagnose a bad carburetor is to eliminate all other possible sources of the problem. If the carburetor is suspected to be the problem, first perform all of the adjustments given in this section. If this doesn't correct the difficulty, then check the ignition system to make sure that the spark plugs, breaker points, and condenser are in good condition and are adjusted to the proper specifications. Check the ignition timing adjustment. Examine the emission control equipment to make sure that all the vacuum lines are connected and none are blocked or clogged (See Emission Controls for more information on emission control equipment). Check all of the vacuum lines on the engine for loose connections, slips or breaks. Tighten the carburetor and intake manifold attaching bolts to the proper specifications. If, after performing all of these checks and adjustments, the problem is still not solved, then it is a good possibility that the carburetor is the source of the problem.

ADJUSTMENTS FOR CARTER AFB



Most of these adjustments require that measurements be gauged in thousandths of an inch. Drill bits are ideal for this purpose.

Float Alignment
  1. Sight down each side of the float shell to determine if the side of the float is parallel to the outer edge of the air horn casting.
  2.  
  3. If the sides are not in alignment, bend the float lever by applying pressure to the end of the float shell while supporting the float lever with your thumb.
  4.  

  1. After aligning the floats, remove as much clearance as possible between the arms of the float lever and the lugs on the air horn. To do this, bend the float lever.
  2.  

Float Level Setting
  1. Invert the air horn with the gasket in place and the float needles seated.
  2.  
  3. Measure between the top of the float at the outer end and the air horn gasket. The gap should be 7 / 32 in. (5.5mm).
  4.  
  5. Check the other float in the same way.
  6.  
  7. If the setting needs adjustment, bend the float arm to obtain proper adjustment.
  8.  

Float Drop Setting
  1. Hold the air horn in an upright position. Measure the gap between the top of the floats at the outer ends and the air horn gasket. The gap should be 3 / 4 in. (19mm).
  2.  

  1. If an adjustment is necessary, bend the stop tabs on the float levers.
  2.  

Accelerator Pump

This procedure is performed with the air horn installed.

  1. Back off the idle speed adjusting screw until the throttle valves are completely closed.
  2.  
  3. Measure the distance from the top of the air horn to the top of the plunger shaft using a T-scale. The distance should be 7 / 16 in. (11mm).
  4.  

  1. If an adjustment is necessary, bend the pump rod at the lower angle with a needle-nosed pliers.
  2.  
  3. Re-adjust the curb idle.
  4.  

Secondary Throttle Lever
  1. Remove the carburetor from the engine.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Invert the carburetor and slowly open the primary throttle valves until there is a gap of 23 / 64 - 3 / 8 in. (9.2-9.5mm) between the lower edge of the primary valve and the bore opposite the idle port. At this point the secondary throttle valves should just start to open. The stop lugs on both primary and secondary throttle levers should contact the bosses on the flange at the same time.
  2.  
  3. If an adjustment is necessary, bend the secondary throttle operating rod at the angle with a needle-nosed pliers. At wide-open throttle, both primary and secondary throttle valves should be vertical.
  4.  
  5. With the primary and secondary throttle valves closed, it should be possible to insert wire gauge tool No.
  6.  

T-109-29 or equivalent, between the positive closing shoes on the primary and secondary levers.

  1. If an adjustment is necessary, bend the shoe on the primary lever until the correct clearance is reached.
  2.  

ADJUSTMENTS FOR CARTER BBS



Most of these adjustments require that measurements be gauged in thousandths of an inch. Drill bits are ideal for this purpose.

Accelerator Pump And Bowl Vent
  1. Back off the idle speed screw and open the choke valve so that when the throttle valves are closed the fast idle adjustment screw does not contact the fast idle cam.
  2.  

  1. Be sure that the pump operating rod is in the medium stroke hole (long hole for the BBS-4340S and BBS-4341S) in the throttle lever and that the bowl vent clip on the pump stem is in the center notch (lower notch on the BBS-4340S and BBS-4341S).
  2.  
  3. Close the throttle valves tightly. It should just be possible to insert a 1 / 16 in. (1.5mm) gauge between the bowl vent and the air horn 27 / 32 in. (21.4mm) on the BBS-3277S accelerator pump plunger travel).
  4.  
  5. If an adjustment is necessary, bend the pump operating rod at the lower angle.
  6.  

Fast Idle Cam Position Automatic Choke
  1. Adjust the fast idle speed as described later.
  2.  
  3. Place the fast idle screw on the second highest step of the fast idle cam.
  4.  
  5. Move the choke valve towards the closed position using light pressure on the choke shaft lever.
  6.  
  7. Insert a 5 / 64 in. (2mm) wire gauge between the choke valve and the wall of the air horn. If an adjustment is necessary, bend the fast idle rod at the upper angle.
  8.  

Vacuum Kick
  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 10 in. Hg (34 kPa) for trucks through 6575 or to 67 in. Hg (51 kPa) for 6576 and later trucks.
  4.  
  5. Insert a 7 / 64 in. (2.8mm) gauge between the choke valve and the wall of the air horn.
  6.  
  7. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  8.  
  9. Remove the gauge. If a slight drag is not felt as the gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  10.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  

Choke Unloader

The choke unloader adjustment is a mechanical device that partially opens the choke valve at wide-open throttle. It should be adjusted as follows:

  1. Hold the throttle valve in the wide-open position.
  2.  
  3. Insert a 3 / 16 in. (4.7mm) gauge between the upper edge of the choke valve and the wall of the air horn.
  4.  

  1. While pressing lightly against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  2.  
  3. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  4.  

Fast Idle Speed
  1. Run the engine until it reaches normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly.
  4.  
  5. On models without the Clean Air Package, close the choke plate about 20°, then allow the throttle plates to close. The fast idle screw should now rest on the slowest speed step of the cam. On models with the Clean Air Package, close the choke plate until the fast idle screw can be positioned on the second highest speed step of the cam.
  6.  
  7. Start the engine.
  8.  
  9. Turn the fast idle speed screw in or out until the specified speed is obtained.
  10.  
  11. Stopping the engine between adjustments is not necessary. However, be sure the fast idle speed screw is positioning on the cam after each speed adjustment.
  12.  

Spring Staged Choke
  1. Push on the choke hub lever with your finger, at the closed position. A small opening should exist between the shaft and hub levers.
  2.  
  3. Using a gauge bit, measure the opening. The opening should be 0.010-0.040 in. (0.25-1.00mm).
  4.  
  5. If not, bend the hub lever tang until the correct opening is reached.
  6.  

Dashpot

This procedure is performed on manual transmissions only.

  1. With the idle speed and mixture properly set, position the throttle lever so that the actuating tab on the lever contacts the stem of the dashpot, but does not depress it.
  2.  
  3. The engine speed should be 1,000 rpm. To adjust the setting, loosen the locknut, then screw the dashpot in or out as required. When the correct setting has been obtained, tighten the locknut against the bracket.
  4.  

Float

This procedure can be performed without removing the carburetor from the engine.

  1. Remove the accelerator pump operating rod.
  2.  
  3. Remove 2 of the long air horn screws and 2 of the short screws. Install the 2 short screws in place of the long screws. This will hold the main body to the throttle body. Tighten the screws securely.
  4.  
  5. Remove the remaining air horn screws.
  6.  
  7. Tilt the air horn far enough to disengage the fast idle cam link from the fast idle cam. Remove the air horn and gasket.
  8.  
  9. Seat the float fulcrum pin by pressing on the fulcrum pin retainer. There should be enough fuel in the bowl to raise the float so that the lip bears firmly against the needle. Additional fuel may be entered by slightly depressing the float. If there is not enough pressure in the line to enter more fuel, you'll have to add some from a clean container.
  10.  


CAUTION
Never smoke when working around gasoline! Avoid all sources of sparks or ignition. Gasoline vapors are EXTREMELY volatile!

  1. With the fuel level holding the tip of the float against the inlet needle, check the gap between the gasket surface of the bowl (gasket removed) and the center crown of the floats. The gap should be 1 / 4 in. ( 6mm) on BBS models 677S, 4342S and 4341S; 7 / 32 in. (5.5mm) on models 4340S and 3277S.
  2.  
  3. If adjustment is necessary, hold the float on the bottom of the bowl and bend the float tip toward or away from the needle as required. Recheck the gap.
  4.  


WARNING
Do not allow the float lip to depress the needle, as this will give you a false reading.When correctly set, the float lip should be perpendicular to the needle within 10°.

  1. Assemble the air horn.
  2.  
  3. Check the idle speed.
  4.  

ADJUSTMENTS FOR CARTER BBD



Most of these adjustments require that measurements be gauged in thousandths of an inch. Drill bits are ideal for this purpose.

Accelerator Pump
1967-72
  1. Back off the idle speed screw.
  2.  
  3. Make sure that the pump connector rod is in the center hole of the throttle lever.
  4.  
  5. Close the throttle valves tightly. On all models, except those with 8-383 engine, it should just be possible to insert a 1 / 64 in. (0.39mm) gauge between the top of the air horn and the end of the plunger shaft. On the 8-383 without the Clean Air Package, the gap should be 29 / 32 in. (23mm); or 1 in. (25mm) on Clean Air Package models.
  6.  
  7. If an adjustment is necessary, bend the pump operating rod at the lower angle.
  8.  
  9. Reset the idle.
  10.  

1973-84

See Figure 1

  1. Remove the cover plate.
  2.  
  3. Back off the idle speed screw to completely close the throttle plate.
  4.  
  5. Open the choke plate so that the fast idle cam allows the throttle plates to seat in their bores.
  6.  



Click image to see an enlarged view

Fig. Fig. 1: Accelerator pump stroke measurement

  1. Turn the curb idle adjusting screw clockwise until it just contacts the stop, then, turn it 2 full turns further.
  2.  
  3. Make sure that the accelerator pump S-link is in the outer hole of the pump arm.
  4.  
  5. Measure the distance between the surface of the air horn and the top of the accelerator pump shaft. The gap should be 1 / 2 in. (12mm).
  6.  
  7. To adjust the pump travel, loosen the pump arm adjusting lockscrew and rotate the sleeve until the proper gap is reached. Then tighten the lockscrew.
  8.  

If the accelerator pump stroke adjustment is changed, the bowl vent valve adjustment must be reset.

Fast Idle Cam-Automatic Choke

See Figure 2

  1. Adjust the fast idle speed (as described later in this section).
  2.  
  3. Place the fast idle screw on the second highest step of the fast idle cam.
  4.  
  5. Move the choke valve towards the closed position using light pressure on the choke shaft lever.
  6.  



Click image to see an enlarged view

Fig. Fig. 2: Fast idle cam position adjustment-1973 and later vehicles

  1. Insert a 5 / 64 in. (2mm) gauge between the choke valve and the wall of the air horn on models through 6572. On 6573-84 models use a 0.110 in. (2.7mm) gauge on carburetor. models 8147S; an 0.070 in. (1.7mm) gauge on all other models. If an adjustment is necessary, bend the fast idle rod at the upper angle.
  2.  

Vacuum Kick

See Figure 3

  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 10 in. Hg (34 kPa) for trucks through 6575 or to 67 in. Hg (51 kPa) for 6576 and later trucks.
  4.  



Click image to see an enlarged view

Fig. Fig. 3: Choke vacuum kick adjustment-1973-84

  1. Insert the specified gauge between the choke valve and the wall of the air horn:

    Models through 6572- 0.109 in. (2.7mm)
     
    Models 6573 though 6579- 0.110 in. (2.7mm)
     
    Models 6580 through 6584- 0.070 in. (1.7mm)
     
    Model 8146S - 0.150 in. (3.8mm)
     
    Model 8147S- 0.130 in. (3.3mm)
     

  2.  
  3. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  4.  
  5. Remove the gauge bit. If a slight drag is not felt as the gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  6.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  

Choke Unloader

See Figure 4

The choke unloader adjustment is a mechanical device that partially opens the choke valve at wide-open throttle. It should be adjusted as follows:

  1. Hold the throttle valve in the wide-open position.
  2.  



Click image to see an enlarged view

Fig. Fig. 4: Choke unloader adjustment-1980-84

  1. Insert a gauge between the upper edge of the choke valve and the wall of the air horn:
  2.  



Models through 6572- 0.16 in. (4.0mm)
 
Models 6573 through 79- 0.28 in. (7.1mm)
 
Models 6580 through 81- 0.31 in. (7.8mm)
 
Models 6582 through 84- 0.31 in. (7.8mm)
 

  1. While pressing lightly against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  2.  
  3. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  4.  

Bowl Vent Valve

See Figure 5

  1. Remove the vent valve cover.
  2.  
  3. Hold the throttle plates closed. It should be possible to insert a 0.060 in. (1.5mm) gauge between the bowl vent valve and the air horn on models though 6579; or a 0.080 in. (2.0mm) gauge on 6580-84 models.
  4.  



Click image to see an enlarged view

Fig. Fig. 5: Bowl vent valve adjustment-1980-84

  1. If adjustment is necessary, bend the short tang on the vent operating lever until the proper clearance is reached.
  2.  

Float

See Figures 6, 7 and 8

This procedure is performed with the carburetor on the engine.



Click image to see an enlarged view

Fig. Fig. 6: Float adjustment on later models

  1. Remove the clips, then disengage the accelerator pump operating rod from the throttle lever and the pump rocker arm.
  2.  
  3. Remove the fast idle cam retaining clip, then remove the link.
  4.  
  5. Remove the step-up piston cover plate and gasket from the air horn top.
  6.  
  7. Remove the metering rod lifter lockscrew, then lift the step-up piston and metering rod assembly straight up and out of the air horn.
  8.  
  9. Remove the air horn retaining screws and lift the air horn straight up and away from the main body.
  10.  
  11. Remove the float baffle.
  12.  
  13. Seat the float fulcrum pin by pressing on the fulcrum pin retainer. There should be enough fuel in the bowl to raise the float so that the lip bears firmly against the needle. Additional fuel may be entered by slightly depressing the float. If there is not enough pressure in the line to enter more fuel, you'll have to add some from a clean container.
  14.  



Click image to see an enlarged view

Fig. Fig. 7: Float setting adjustment


CAUTION
Never smoke when working around gasoline! Avoid all sources of sparks or ignition. Gasoline vapors are EXTREMELY volatile!

  1. With the fuel level holding the tip of the float against the inlet needle, check the gap between the gasket surface of the bowl (gasket removed) and the center crown of the floats. On models through 6572, the gap should be 15 / 64 in. (5.9mm) on models with a manual choke; 5 / 16 in. (7.9mm) on models with an automatic choke. On later models, the gap should be 1 / 4 in. (6.3mm).
  2.  
  3. If adjustment is necessary, hold the float on the bottom of the bowl and bend the float tip toward or away from the needle as required. Recheck the gap.
  4.  



Click image to see an enlarged view

Fig. Fig. 8: Checking your float setting


WARNING
Do not allow the float lip to depress the needle, as this will give you a false reading.

When correctly set, the float lip should be perpendicular to the needle within 10°.

  1. Assemble the air horn.
  2.  
  3. Check the idle speed.
  4.  

Fast Idle Speed

See Figure 9

  1. Run the engine until it reaches normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly.
  4.  
  5. On models without the Clean Air Package, close the choke plate about 20°, then allow the throttle plates to close. The fast idle screw should now rest on the slowest speed step of the cam. On models with the Clean Air Package, close the choke plate until the fast idle screw can be positioned on the second highest speed step of the cam.
  6.  



Click image to see an enlarged view

Fig. Fig. 9: Fast idle speed adjustment-1973-84

  1. Start the engine.
  2.  
  3. On trucks through 6572, turn the fast idle speed screw in or out until 1,700 rpm is obtained for carburetor model 2536S; 1,500 rpm for all other models. On 6573-84 models, check your underhood sticker for the proper speed.
  4.  
  5. Stopping the engine between adjustments is not necessary. However, be sure the fast idle speed screw is positioned on the cam after each speed adjustment.
  6.  

ADJUSTMENTS FOR CARTER THERMO-QUAD



Most of these adjustments require that measurements be gauged in thousandths of an inch. Drill bits are ideal for this purpose.

See Figure 10



Click image to see an enlarged view

Fig. Fig. 10: Carter Thermo-Quad carburetor

Float Setting

See Figure 11

  1. Remove the bowl cover and invert it.
  2.  
  3. Place the gasket on the cover and, with the floats resting on the needle, check the distance from the gasket surface to the float bottom (currently the top side) on each float. The distance should be 29 / 32 in. plus or minus 1 / 32 in.
  4.  
  5. If not, bend the float lever arm.
  6.  



Click image to see an enlarged view

Fig. Fig. 11: Float setting adjustment


WARNING
Never allow the float lever to depress the needle when measuring or adjusting!

Secondary Throttle Linkage

See Figure 12

  1. Remove the carburetor.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Hold the fast idle lever in the curb idle position and invert the carburetor.
  2.  
  3. Slowly open the primary throttle plates to the wide-open position. The primary and secondary levers should both contact the stops at the same time.
  4.  



Click image to see an enlarged view

Fig. Fig. 12: Secondary throttle linkage adjustment

  1. If an adjustment is necessary, bend the secondary throttle operating rod at the angle.
  2.  

Secondary Air Valve Opening

See Figure 13

  1. With the air valve in the wide-open position, the gap between the air valve (at the short side) and the air horn should be set to the specifications for your carburetor. Please refer to the carburetor specifications charts found later in this section.
  2.  



Click image to see an enlarged view

Fig. Fig. 13: Secondary air valve opening adjustment-1982

  1. If not, the corner of the air valve is notched for adjustment. Bend the corner with a needle-nosed pliers for proper adjustment.
  2.  

Secondary Air Valve Spring Tension

See Figure 14


WARNING
Hold the air valve adjustment plug with a screwdriver while loosening the lock plug to avoid the spring's snapping out of position. If the spring snaps out, you'll have to disassemble the carburetor!

  1. Loosen the air valve lock plug and allow the valve to go to the wide-open position.
  2.  



Click image to see an enlarged view

Fig. Fig. 14: Secondary air valve spring tension adjustment-1982 carburetor

  1. Using a long screwdriver and tool C-4152 on the plug, turn the plug counterclockwise until the air valve contacts its stop lightly, then rotate the plug any additional turns as necessary for specification. Please refer to the carburetor specifications charts found later in this section.
  2.  
  3. Hold the adjustment plug securely and tighten the lock plug with tool C-4152, make sure the adjustment does not move.
  4.  
  5. Check the air valve for freedom of movement.
  6.  

Accelerator Pump Stroke
FIRST STAGE

See Figures 15 and 16

  1. Be sure that the throttle connector rod is in the center hole of the pump arm, or the inner hole on 2-hole arms.
  2.  
  3. Measure the height of the accelerator pump plunger link at curb idle. On trucks with a solenoid idle stop, the ignition switch should be in the ON position.
  4.  



Click image to see an enlarged view

Fig. Fig. 15: Accelerator pump stroke adjustment

  1. The height should be adjusted to specifications. If not, bend the throttle connector rod at the second angle from the top.
  2.  

SECOND STAGE
  1. Open the choke, then open the throttle until the secondary lockout latch is just applied. Downward travel of the plunger stops at this point.
  2.  



Click image to see an enlarged view

Fig. Fig. 16: Accelerator pump assembly

  1. Measure the height of the pump plunger link. The height should be 5 / 16 in. (7.9mm). If not, bend the tang at the bottom of the throttle lever.
  2.  

Choke Control Lever

See Figure 17

  1. Remove the carburetor.
  2.  

Use rags to catch any remaining fuel.

  1. Place the carburetor on a clean, flat surface. The surface must be flush with the bottom of the flange and extend out under the choke control lever.
  2.  



Click image to see an enlarged view

Fig. Fig. 17: Choke control lever adjustment

  1. Close the choke by pushing the lever with the throttle partially open.
  2.  
  3. Measure the vertical distance from the top of the rod hole in the control lever, down to the flat surface on which the carburetor is resting. The distance should be 3 3 / 8 in. (85mm).
  4.  
  5. If not, bend the link connecting the two choke shafts at the upper angle.
  6.  

If you change this adjustment, you'll have to reset the vacuum kick, fast idle cam and choke unloader adjustments.

Choke Diaphragm Connector Rod

See Figure 18

  1. Fully depress the diaphragm stem, either using a vacuum source, or by hand.
  2.  
  3. With light opening pressure on the air valve connector rod, check the gap between the air valve and its stop. The gap should be 0.040 in. (1.0mm).
  4.  



Click image to see an enlarged view

Fig. Fig. 18: Choke diaphragm connector rod adjustment

  1. If not, bend the diaphragm control rod at its angle.
  2.  

If you change this setting, you'll have to adjust the vacuum kick.

Choke Vacuum Kick

See Figure 19

  1. Remove the carburetor.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Using a vacuum source, or by hand, fully depress the vacuum diaphragm plunger.
  2.  
  3. Using a 0.16 in. (4.mm) gauge for 66 states and Canada, or 0.10 in. (2.5mm) for California, measure between the lower edge of the choke plate and the air horn wall at a point close to the outboard end.
  4.  



Click image to see an enlarged view

Fig. Fig. 19: Choke vacuum kick adjustment


CAUTION
Do not change position of choke with the gauge during measurement.

  1. Adjust by twisting a screwdriver into the tang slot. DO not adjust diaphragm rod.
  2.  
  3. Check for free movement between open and adjust positions. Correct any misalignment or interference and repeat the adjustment if needed.
  4.  

Fast Idle Cam Position

See Figure 20

  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  
  3. Measure by inserting a 0.310 in. (7.8mm) gauge between the bottom of the choke valve and air horn wall at the throttle lever side.
  4.  



Click image to see an enlarged view

Fig. Fig. 20: Fast idle cam position adjustment

  1. If adjustment is necessary, bend the fast idle link at the angle until the correct valve opening has been obtained.
  2.  

When this adjustment is made, the choke unloader adjustment and secondary throttle lockout adjustment must be reset.

Choke Unloader

See Figure 21

  1. Hold the throttle valves in the wide-open position.
  2.  



Click image to see an enlarged view

Fig. Fig. 21: Choke unloader adjustment

  1. Press lightly against the choke lever while measuring by inserting the specified gauge between the bottom of the choke valve and air horn wall (at the throttle lever side).
  2.  
  3. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  4.  

Secondary Throttle Lockout

See Figure 22

  1. Move the fast idle control lever to the open choke position.
  2.  
  3. Measure the clearance between the lockout lever and the stop. The gap should be 0.06-0.09 in. (1.5-2.2mm).
  4.  



Click image to see an enlarged view

Fig. Fig. 22: Secondary throttle lockout adjustment

  1. If not, bend the tang on the fast idle control lever.
  2.  

Fast Idle Speed

See Figure 23

  1. Run the engine to normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly. Remove the air cleaner and disconnect the vacuum lines to the heated air control and the Orifice Spark Advance Control (OSAC) valve. If not equipped with an OSAC valve, disconnect the distributor vacuum advance line. Disconnect the EGR hose. Cap all carburetor vacuum fittings.
  4.  
  5. Start the engine. Adjust the idle speed and mixture, if necessary.
  6.  
  7. Close the throttle plates until the fast idle screw is positioned on the second highest speed step of the cam.
  8.  



Click image to see an enlarged view

Fig. Fig. 23: Fast idle speed adjustment

  1. Turn the fast idle speed screw in or out to obtain the correct speed, adjustment procedures are located on the emissions label.
  2.  
  3. Stopping the engine between adjustments is not necessary. However, be sure the fast idle speed screw is positioned on the cam after each speed adjustment.
  4.  

Vacuum Throttle Positioner
  1. Run the engine to normal operating temperature.
  2.  
  3. With the transmission in Neutral and the brakes applied, accelerate the engine to above 2,000 rpm. Check that the vacuum positioner unit operates and can withstand a hand-applied load in the operating position. If not, replace the positioner.
  4.  
  5. Accelerate the engine, by hand-moving the linkage, to 2,500 rpm.
  6.  
  7. Loosen the positioner adjustment locknut, then rotate the positioner assembly until it just contacts the throttle lever.
  8.  
  9. Release the throttle lever and slowly adjust the positioner to decrease the engine speed until a sudden drop in engine speed occurs, above 1,000 rpm. At this point, continue turning the positioner, in the decreasing direction, an additional 1 / 4 turn. Hold the positioner and tighten the locknut.
  10.  
  11. Accelerate the engine, by hand, to 2,500 rpm and release the throttle. The engine should return to normal idle.
  12.  

ADJUSTMENTS FOR HOLLEY 6545



Most of these adjustments require that measurements be gauged in thousandths of an inch. Drill bits are ideal for this purpose.

Float Setting
  1. Remove the carburetor.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Remove the float bowl cover. Drain all fuel from the bowl.
  2.  
  3. Place the gasket on the float bowl, then invert the bowl. Hold the retaining spring in place.
  4.  
  5. Place a straightedge across the surface of the bowl. It should just touch the floats. A tolerance of 1 / 32 in. (0.8mm) is allowable.
  6.  
  7. If adjustment is necessary, bend the float tang to obtain the correct adjustment.
  8.  

Accelerator Pump Piston Stroke

See Figure 24

  1. Place the throttle linkage in the curb idle position.
  2.  
  3. Place the pump operating link in the middle slot on carburetor model R-7847-A, or in the left slot on all others.
  4.  
  5. With a T-scale, measure the length of the pump operating link. On models through 6572, the link should be 2 7 / 32 in. (2.21mm) on R-7847-A models; 2 21 / 64 in. (2.32mm) on all other models. On 6573-79 models, the link should be 2 7 / 32 in. (2.21mm) for trucks with manual transmission, or 2 11 / 32 in. (2.34mm) for trucks with automatic transmission. On 6580 and later trucks, the link should be 1 5 / 8 in. (1.62mm).
  6.  



Click image to see an enlarged view

Fig. Fig. 24: Accelerator pump piston stroke adjustment

  1. To adjust, bend the link at the angle.
  2.  

Fast Idle Cam Position
  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  
  3. Insert a 0.08 in. (2mm) gauge between the upper edge of the choke plate and the wall of the air horn.
  4.  
  5. If adjustment is necessary, bend the fast idle link at the angle until the gauge fits between the choke plate and the wall of the air horn.
  6.  

Choke Unloader

See Figure 25

  1. Hold the throttle valve in the wide-open position.
  2.  
  3. With a light closing pressure against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  4.  
  5. Measure by inserting a 0.250 in. (6.3mm) gauge between the top of the choke valve and air horn wall at the throttle lever side.
  6.  



Click image to see an enlarged view

Fig. Fig. 25: Choke unloader adjustment

  1. Adjust by bending the tang on the throttle lever.
  2.  

Choke Vacuum Kick

See Figure 26

  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  



Click image to see an enlarged view

Fig. Fig. 26: Choke vacuum kick adjustment

  1. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 67 in. Hg (51 kPa).
  2.  

  1. On models through 6572, insert a 0.11 in. (2.7mm) gauge between the choke valve and the wall of the air horn. On 6573-77 models, use a 0.14 in. (3.5mm) gauge for manual transmission trucks or 0.09 in. (2.2mm) for automatic transmission trucks. On 6578-79 models, use a 0.10 in. (2.5mm) gauge bit. On 6580 and later models, use a 0.13 in. (3.3mm) gauge bit.
  2.  
  3. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  4.  
  5. Remove the gauge bit. If a slight drag is not felt as the gauge or gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  6.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  

Fast Idle Speed
  1. Run the engine to normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly. Remove the air cleaner and disconnect the vacuum lines to the heated air control and the Orifice Spark Advance Control (OSAC) valve. If not equipped with an OSAC valve, disconnect the distributor vacuum advance line. Disconnect the EGR hose. Cap all carburetor vacuum fittings.
  4.  
  5. Close the choke plate until the fast idle screw can be positioned on the second highest speed step of the cam.
  6.  
  7. Start the engine and determine the idle speed.
  8.  
  9. Turn the fast idle speed screw in or out until the speed shown on your truck's underhood sticker is obtained.
  10.  
  11. Stopping the engine between adjustments is not necessary. However, be sure the fast idle speed screw is positioned on the cam after each speed adjustment.
  12.  

Dashpot

See Figure 27

This procedure is for manual transmissions only.

  1. Set the curb idle and mixture.
  2.  
  3. Start the engine and position the throttle lever so that the actuating tab on the lever is contacting the stem of the dashpot without depressing it.
  4.  
  5. Allow about 30 seconds for the engine speed to stabilize. The engine speed should be 2,500 rpm.
  6.  



Click image to see an enlarged view

Fig. Fig. 27: Dashpot adjustment-manual transmission

  1. If not, loosen the locknut and turn the dashpot in or out as necessary.
  2.  
  3. Hold the dashpot and tighten the locknut.
  4.  

ADJUSTMENTS FOR HOLLEY 2210



Fast Idle Cam Position
  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  
  3. Insert a 0.11 in. (2.7mm) gauge between the upper edge of the choke plate and the wall of the air horn.
  4.  
  5. If adjustment is necessary, bend the fast idle link at the angle until the specified gauge fits between the choke plate and the wall of the air horn.
  6.  

Vacuum Kick
  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 67 in. Hg (51 kPa).
  4.  
  5. Insert a 0.15 in. (3.8mm) gauge between the choke valve and the wall of the air horn.
  6.  
  7. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  8.  
  9. Remove the gauge bit. If a slight drag is not felt as the gauge or gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  10.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  

Choke Unloader
  1. Hold the throttle valve in the wide-open position.
  2.  
  3. With light closing pressure against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  4.  
  5. Measure by inverting a 0.170 in. (4.3mm) gauge between the top of the choke valve and air horn wall at the throttle lever side.
  6.  
  7. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  8.  

Accelerator Pump Stroke
  1. Make sure that the pump connector rod is in the first slot (closest to the retaining nut) of the pump arm.
  2.  
  3. Measure the travel (drop) of the accelerator pump plunger between curb idle, or closed throttle, and wide-open throttle. Closed idle is obtained by backing off the curb idle screw and moving the fast idle cam to open chock position. To adjust pump travel, bend the pump operating rod in the proper area until the correct setting has been obtained.
  4.  
  5. Travel should be 0.26 in. (6.6mm) for curb idle through wide-open throttle, or 0.31 in. (7.8mm) for closed throttle through wide-open throttle.
  6.  
  7. If not, bend the pump operating rod at the angle.
  8.  

Fast Idle Speed
  1. Run the engine until it reaches normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly. Remove the air cleaner and disconnect the vacuum lines to the heated air control and the Orifice Spark Advance Control (OSAC) valve. If not equipped with an OSAC valve, disconnect the distributor vacuum advance line. Disconnect the EGR hose. Cap all carburetor vacuum fittings.
  4.  
  5. Close the choke plate until the fast idle screw can be positioned on the second highest speed step of the cam.
  6.  
  7. Start the engine.
  8.  
  9. Turn the fast idle speed screw in or out until the a speed of 1,700 rpm for manual transmissions or 1,800 rpm for automatic transmissions is reached.
  10.  
  11. Stopping the engine between adjustments is not necessary. However, be sure the fast idle speed screw is positioned on the cam after each speed adjustment.
  12.  

Vacuum Throttle Positioner
  1. Run the engine to normal operating temperature.
  2.  
  3. With the transmission in Neutral and the brakes applied, accelerate the engine to above 2,000 rpm. Check that the vacuum positioner unit operates and can withstand a hand-applied load in the operating position. If not, replace the positioner.
  4.  

  1. Accelerate the engine, by hand-moving the linkage, to 2,500 rpm.
  2.  
  3. Loosen the positioner adjustment locknut, then rotate the positioner assembly until it just contacts the throttle lever.
  4.  
  5. Release the throttle lever and slowly adjust the positioner to decrease the engine speed until a sudden drop in engine speed occurs, above 1,000 rpm. At this point, continue turning the positioner, in the decreasing direction, an additional 1 / 4 turn. Hold the positioner and tighten the locknut.
  6.  
  7. Accelerate the engine, by hand, to 2,500 rpm and release the throttle. The engine should return to normal idle.
  8.  

Float Setting
  1. Invert the air horn so that the weight of the float alone is forcing the needle against the seat.
  2.  
  3. Measure the clearance between the top of the float and the float stop. The clearance should be 0.08 in. (2mm).
  4.  

  1. If an adjustment is necessary, bend the flat tab toward or away from the needle using a narrow blade prytool.
  2.  
  3. Check the float drop by holding the air horn in an upright position. The bottom edge of the float should be even with and parallel to the underside surface of the air horn. If necessary, bend the tang on the float arm to make an adjustment.
  4.  

ADJUSTMENTS FOR HOLLEY 2300G



Fast Idle Cam
  1. Adjust the curb idle and mixture.
  2.  
  3. Place the choke in the wide-open position.
  4.  
  5. Adjust the clearance between the fast idle cam and the screw to 0.035 in. (0.8mm).
  6.  

Fuel Level
  1. Place a shop towel under the sight plug to catch any spilled fuel.
  2.  
  3. Start the engine.
  4.  
  5. Remove the sight plug from the fuel bowl.
  6.  
  7. Loosen the lockscrew, then turn the adjusting nut until the fuel just seeps from the sight hole.
  8.  

The truck should be on a level floor.

  1. Tighten the lockscrew while holding the adjusting nut.
  2.  
  3. Install the sight plug.
  4.  

Accelerator Pump Lever Clearance
  1. Hold the throttle plates wide-open while holding the pump lever down. At this point it should be just possible to insert a 0.015 in. (3.8mm) gauge between the adjusting nut and the lever.
  2.  

  1. If not, turn the pump override screw until the correct clearance has been reached.
  2.  

There should be no free movement of the pump lever when the throttle is at curb idle.

Loading The Positive Throttle Return Spring

CAUTION
Whenever the throttle return spring is disconnected at either end, the throttle lever at the carburetor will snap to the closed position with considerable force. This could cause personal injury if your hands are in the way!

To prevent personal injury, perform the following in the order given, and keep your hands clear of the throttle linkage when disconnecting or connecting the return spring.

If the throttle return spring has been disconnected or removed, the throttle linkage will be in the "unloaded'' position. The truck can be driven this way, however an increased throttle effort will be noted.

To load the linkage:
  1. With the engine off, have an assistant fully depress the accelerator pedal. This will rotate the throttle assembly to the wide-open position.
  2.  
  3. Connect the return spring between the trip lever and the anchor bracket. Make sure that the tab is engaged in the notch.
  4.  
  5. Move your hands away and have your assistant let up on the pedal slowly .
  6.  
  7. The linkage is now loaded and normal pedal should be felt.
  8.  

ADJUSTMENTS FOR HOLLEY 2245



See Figure 28



Click image to see an enlarged view

Fig. Fig. 28: Holley 2245 carburetor

Fast Idle Cam Position
  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  
  3. Insert a 0.110 in. (2.7mm) gauge between the top of the choke valve and wall of the air horn.
  4.  
  5. If a slight drag is not felt, it will be necessary to make an adjustment.
  6.  
  7. If adjustment is necessary, bend the fast idle link at the angle until the specified gauge fits between the choke plate and the wall of the air horn.
  8.  

Vacuum Kick

See Figure 29

  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 67 in. Hg (51 kPa).
  4.  
  5. For models through 6577, insert a 0.15 in. (3.8mm) gauge between the choke valve and the wall of the air horn. On 6578 and later models, use a 0.11 in. (2.7mm) gauge.
  6.  



Click image to see an enlarged view

Fig. Fig. 29: Vacuum kick adjustment for choke

  1. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  2.  
  3. Remove the gauge. If a slight drag is not felt as the gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  4.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  
  5. Reinstall vacuum hoses on the correct carburetor fittings.
  6.  

Choke Unloader

See Figure 30

  1. Hold the throttle valve in the wide-open position.
  2.  
  3. Insert a 0.17 in. (4.3mm) gauge between the upper edge of the choke valve and the wall of the air horn.
  4.  



Click image to see an enlarged view

Fig. Fig. 30: Choke unloader (wide-open kick) adjustment

  1. While pressing lightly against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  2.  
  3. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  4.  

Accelerator Pump Stroke
  1. Make sure that the pump connector rod is in the first slot (closest to the retaining nut) of the pump arm.
  2.  
  3. Measure the travel (drop) of the accelerator pump plunger between curb idle, or closed throttle, and wide-open throttle. Closed idle is obtained by backing off the curb idle screw and moving the fast idle cam to open chock position. To adjust pump travel, bend the pump operating rod in the proper area until the correct setting has been obtained.
  4.  
  5. Travel should be 0.26 in. (6.6mm) for curb idle through wide-open throttle, or 0.31 in. (7.8mm) for closed throttle through wide-open throttle.
  6.  
  7. If not, bend the pump operating rod at the angle.
  8.  

Fast Idle Speed

See Figure 31

  1. Run the engine until it reaches normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly. Remove the air cleaner and disconnect the vacuum lines to the heated air control and the Orifice Spark Advance Control (OSAC) valve. If not equipped with an OSAC valve, disconnect the distributor vacuum advance line. Disconnect the EGR hose. Cap all carburetor vacuum fittings.
  4.  



Click image to see an enlarged view

Fig. Fig. 31: Fast idle speed adjustment

  1. Close the choke plate until the fast idle screw can be positioned on the second highest speed step of the cam.
  2.  
  3. Start the engine.
  4.  
  5. Turn the fast idle speed screw in or out until the a speed of 1,700 rpm for manual transmissions or 1,800 rpm for automatic transmissions is reached on models through 6577; 1,600 rpm on 6578 and later models.
  6.  
  7. Stopping the engine between adjustments is not necessary. However, be sure the fast idle speed screw is positioned on the cam after each speed adjustment.
  8.  

Vacuum Throttle Positioner
  1. Run the engine to normal operating temperature.
  2.  
  3. With the transmission in Neutral and the brakes applied, accelerate the engine to above 2,000 rpm. Check that the vacuum positioner unit operates and can withstand a hand-applied load in the operating position. If not, replace the positioner.
  4.  
  5. Accelerate the engine, by hand-moving the linkage, to 2,500 rpm.
  6.  
  7. Loosen the positioner adjustment locknut, then rotate the positioner assembly until it just contacts the throttle lever.
  8.  
  9. Release the throttle lever and slowly adjust the positioner to decrease the engine speed until a sudden drop in engine speed occurs, above 1,000 rpm. At this point, continue turning the positioner, in the decreasing direction, an additional 1 / 4 turn. Hold the positioner and tighten the locknut.
  10.  
  11. Accelerate the engine, by hand, to 2,500 rpm, then release the throttle. The engine should return to normal idle.
  12.  

Float Setting
  1. Remove the air horn.
  2.  
  3. Invert the air horn so that the weight of the float alone is forcing the needle against the seat.
  4.  

  1. Measure the clearance between the top of the float and the float stop. The clearance should be 0.08 in. (2mm) on models through 6577; 0.20 in. (5mm) on 6578 and later models.
  2.  
  3. If an adjustment is necessary, bend the flat tab toward or away from the needle using a narrow blade prytool.
  4.  
  5. Check the float drop by holding the air horn in an upright position. The bottom edge of the float should be even with and parallel to the underside surface of the air horn. If necessary, bend the tang on the float arm to make an adjustment.
  6.  

Float Drop
1978 and Later
  1. Remove the air horn.
  2.  
  3. Allow the float to hang. The bottom of the float should be parallel with the air horn gasket surface.
  4.  
  5. Bend the tang on the float arm to correct the float drop.
  6.  

ADJUSTMENTS FOR HOLLEY 2280



Fast Idle Cam Position

See Figure 32

  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  
  3. Insert a 0.07 in. (1.7mm) gauge between the upper edge of the choke plate and the wall of the air horn. On carburetor No. 6772-A, use a 0.052 in. (1.3mm) gauge.
  4.  



Click image to see an enlarged view

Fig. Fig. 32: Fast idle cam adjustment

  1. If adjustment is necessary, bend the fast idle link at the angle until the specified gauge fits between the choke plate and the wall of the air horn.
  2.  

Vacuum Kick

See Figure 33

  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 67 in. Hg. (51 kPa).
  4.  



Click image to see an enlarged view

Fig. Fig. 33: Choke vacuum kick adjustment

  1. For models R-8999A and R-9000A, insert a 0.13 in. (3.3mm) gauge between the choke valve and the wall of the air horn. On all other models, use a 0.15 in. gauge.
  2.  
  3. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  4.  
  5. Remove the gauge. If a slight drag is not felt as the gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  6.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  

Choke Unloader

See Figure 34

  1. Hold the throttle valve in the wide-open position.
  2.  
  3. On 6580-81 trucks, insert a 0.31 in. (7.8mm) gauge between the upper edge of the choke valve and the wall of the air horn. On 6582-84 models, use a 0.20 in. (5mm) gauge. On 6585-87 models, the gauge is 0.15 in. (3.8mm) for all except carburetor No. 6772-A; which is 0.20 in. (5mm).
  4.  
  5. While pressing lightly against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  6.  



Click image to see an enlarged view

Fig. Fig. 34: Choke unloader adjustment

  1. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  2.  

Mechanical Power Valve

See Figure 35

  1. Remove the bowl vent cover plate, vent valve lever spring and retainer. Remove the vent valve lever and pivot pin.
  2.  
  3. Hold the throttle in the wide-open position.
  4.  



Click image to see an enlarged view

Fig. Fig. 35: Mechanical power valve adjustment

  1. Insert a 5 / 64 in. (1.9mm) Allen wrench in the power valve adjustment screw.
  2.  
  3. Push the screw down, then release it to determine if any clearance exists. Turn the screw clockwise until clearance is zero.
  4.  
  5. Turn the screw 1 turn counterclockwise.
  6.  
  7. Install the bowl vent gasket and cover plate.
  8.  

Accelerator Pump Stroke

See Figure 36

  1. Remove the bowl vent cover plate and vent valve lever spring. Be careful not to dislodge or lose the vent valve retainer.
  2.  
  3. Make sure that the pump connector rod is in the inner slot of the pump arm.
  4.  
  5. Position the throttle at curb idle; the choke must be open and the fast idle cam must be engaged.
  6.  



Click image to see an enlarged view

Fig. Fig. 36: Accelerator pump stroke adjustment, at idle

  1. Place a straightedge on the bowl vent cover surface of the air horn over the accelerator pump connector rod in the center of the bowl.
  2.  
  3. Bend the accelerator pump connector rod until the lever surface is flush with the air horn surface on models through 6585. On 6586-87 models, 0.210 in. (5.3mm) gap.
  4.  
  5. Install the vent valve lever spring and bowl vent cover plate.
  6.  

If this adjustment is changed, both the bowl vent and the mechanical power valve adjustment must be reset.

Fast Idle Speed

See Figure 37

  1. Run the engine to normal operating temperature.
  2.  
  3. Remove the air cleaner, then disconnect and plug the EGR vacuum line and distributor advance vacuum line. If the engine has Electronic Spark Control, remove only the top of the air cleaner housing and lift the air cleaner to access the carburetor. Do not disconnect the vacuum line to the spark control computer. Instead, use a jumper wire to ground the idle stop switch.
  4.  
  5. Set the parking brake and place the transmission in Neutral. With the engine off, open the throttle and close the choke, then close the throttle.
  6.  



Click image to see an enlarged view

Fig. Fig. 37: Fast idle speed

  1. Rotate the fast idle cam until the fast idle screw can be positioned on the second highest speed step of the cam.
  2.  
  3. Start the engine. Let the engine speed stabilize. If the engine speed continues to rise, the idle switch has not been properly grounded.
  4.  
  5. Turn the fast idle speed screw in or out until the engine speed listed on your truck's underhood sticker is reached.
  6.  
  7. Reposition the screw on the cam after each adjustment in order to allow the idle to properly stabilize.
  8.  
  9. Remove the jumper wire, reconnect the vacuum hoses and install the air cleaner.
  10.  

Float Setting

See Figure 38



Click image to see an enlarged view

Fig. Fig. 38: Float setting adjustment

  1. Remove the carburetor.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Remove the air horn.
  2.  
  3. Invert the carburetor body.
  4.  

The pump intake check ball will drop out. Be sure to catch it!

  1. Allow the weight of the floats to rest on the needle valve. Hold your finger against the hinge pin retainer to fully seat it in the float pin cradle.
  2.  
  3. Using a T-scale, measure the gap between the surface of the float bowl and the toe of each float. The gap should be 1 / 4 - 5 / 16 in. (6.35-7.94mm).
  4.  
  5. If adjustment is necessary, bend the float tang. Bend either float arm to equalize the individual float positions.
  6.  

Bowl Vent Valve
  1. Remove the bowl vent valve cover plate and the vent lever spring.
  2.  


WARNING
Don't dislodge the vent valve lever retainer/pivot pin.

  1. With the throttle in the curb idle position (choke open and the fast idle cam disengaged), press down firmly on the vent valve lever where the spring seats. Simultaneously, press down on the vent valve tang until the vent valve is lightly seated.
  2.  

If this adjustment is being performed with the carburetor off-engine, the carburetor must be on a raised flat surface so that the curb idle throttle plate position is not changed.

  1. While holding the lever and tang down, measure the gap between the contact surfaces of the vent valve lever and the vent valve tang. The gap should be 0.03 in. (0.7mm).
  2.  
  3. If not, adjust by bending the end of the vent valve lever.
  4.  
  5. Install the lever spring and cover.
  6.  

If this adjustment is changed, the accelerator pump adjustment must be reset.

ADJUSTMENTS FOR HOLLEY 250G



Fast Idle
  1. Set the curb idle speed to the specifications listed on the emissions label.
  2.  
  3. Place the choke plate in the fully open position.
  4.  
  5. Place the throttle plates in the curb idle position.
  6.  

  1. Adjust the fast idle stud to give a clearance of 0.035 in. (0.88mm) between the stud and the fast idle cam.
  2.  

Fuel Level
  1. Place a shop towel under the sight plug to catch any spilled fuel.
  2.  
  3. Start the engine.
  4.  

  1. Remove the sight plug from the fuel bowl.
  2.  
  3. Loosen the lockscrew, then turn the adjusting nut until the fuel just seeps from the sight hole.
  4.  

The truck should be on a level floor.

  1. Tighten the lockscrew while holding the adjusting nut.
  2.  
  3. Install the sight plug and tighten securely.
  4.  

Accelerator Pump Lever Clearance
  1. Hold the throttle plates wide-open while holding the pump lever down. At this point it should be just possible to insert a 0.015 in. (0.38mm) gauge between the adjusting nut and the lever.
  2.  
  3. If not, turn the pump override screw until the correct clearance has been reached.
  4.  

There should be no free movement of the pump lever when the throttle is at curb idle.

ADJUSTMENTS FOR HOLLEY 6145



See Figure 39



Click image to see an enlarged view

Fig. Fig. 39: Side views of the Holley 6145 carburetor and components

Fast Idle Cam

See Figure 40

  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  



Click image to see an enlarged view

Fig. Fig. 40: Adjustment of fast idle cam

  1. Insert a 0.07 in. (1.7mm) gauge between the upper edge of the choke plate and the wall of the air horn on trucks with automatic transmission; 0.06 in. (1.5mm) on trucks with manual transmission.
  2.  
  3. If adjustment is necessary, bend the fast idle link at the angle until the specified gauge fits between the choke plate and the wall of the air horn.
  4.  

Vacuum Kick

See Figure 41

  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 67 in. Hg (51 kPa).
  4.  



Click image to see an enlarged view

Fig. Fig. 41: Choke vacuum kick adjustment

  1. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  2.  
  3. Using a 5 / 64 in. (1.9mm) Allen wrench in the diaphragm adjuster, adjust the clearance so that a 0.15 in. (3.8mm) gauge can fit between the choke valve and the wall of the air horn.
  4.  
  5. Remove the gauge.
  6.  
  7. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  8.  
  9. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  10.  

Choke Unloader
  1. Hold the throttle valve in the wide-open position.
  2.  
  3. Insert a 1 / 4 in. (6mm) gauge between the upper edge of the choke valve and the wall of the air horn.
  4.  
  5. While pressing lightly against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  6.  
  7. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  8.  

Accelerator Pump Stroke

See Figure 42

  1. Place the throttle in the curb idle position with the accelerator pump operating link in the #2 (upper) hole in the throttle lever.
  2.  
  3. Measure the length of the operating link. The length should be 1.61 in. (40.8mm) on 6583-84 models; 1.75 in. (44.4mm) on 6585-87 models. If not, bend it at the U-bend.
  4.  



Click image to see an enlarged view

Fig. Fig. 42: Adjusting the accelerator pump stroke clearance

Fast Idle Speed
  1. Run the engine to normal operating temperature.
  2.  
  3. Remove the air cleaner, then disconnect and plug the EGR vacuum line. Disconnect the vacuum hose at the heated air temperature sensor. Plug the hose. Disconnect and plug the 3 / 16 in. (4.7mm) hose at the charcoal canister. Remove the PCV valve from the rocker cover and allow it to draw fresh air.
  4.  
  5. Disconnect and plug the vacuum advance hose at the distributor. Disconnect the engine harness lead at the oxygen sensor. Ground the harness lead. Allow the engine to run for at least 2 minutes after disconnecting the O 2 sensor.
  6.  

Don't put any stress on the oxygen sensor lead!

  1. Open the throttle slightly and place the fast idle screw on the second highest speed step of the cam.
  2.  
  3. With the choke fully open, turn the fast idle speed screw in or out until the engine speed listed on your truck's underhood sticker is reached.
  4.  
  5. Reposition the screw on the cam after each adjustment in order to allow the idle to properly stabilize.
  6.  
  7. Remove the jumper wire, reconnect the vacuum hoses and install the air cleaner.
  8.  

Float Setting

See Figure 43

  1. Remove the carburetor.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Remove the air horn.
  2.  
  3. Drain the float bowl of fuel.
  4.  



Click image to see an enlarged view

Fig. Fig. 43: Float setting adjustment

  1. Invert the carburetor body.
  2.  

The pump intake check ball will drop out. be sure to catch it!

  1. Allow the weight of the floats to rest on the needle valve. Hold your finger against the hinge pin retainer to fully seat it in the float pin cradle.
  2.  
  3. Using a straightedge, the floats should just touch the straightedge at the point on the floats farthest from the fuel inlet.
  4.  
  5. If adjustment is necessary, bend the float tang. Bend either float arm to equalize the individual float positions.
  6.  

Idle Stop Solenoid

See Figure 44

  1. Run the engine to normal operating temperature.
  2.  
  3. Disconnect and plug the EGR vacuum line. Connect a jumper wire between the carburetor switch and a good ground. Disconnect and plug the 3 / 16 in. (4.7mm) hose at the charcoal canister. The air cleaner must not be removed, but should be propped up to gain access to the carburetor. Remove the PCV valve from the rocker cover and allow it to draw fresh air.
  4.  



Click image to see an enlarged view

Fig. Fig. 44: Adjusting the idle stop solenoid

  1. Turn on the air conditioning and set the blower to Low .
  2.  
  3. Disconnect the compressor clutch wire.
  4.  
  5. On models without air conditioning, connect a jumper wire between the battery positive pole and the solenoid idle stop lead wire.
  6.  
  7. Open the throttle slightly and allow the plunger to extend.
  8.  
  9. Remove the adjusting screw and spring from the solenoid.
  10.  
  11. Insert a 1 / 8 in. (3mm) Allen wrench into the solenoid and adjust the engine speed to 290 rpm.
  12.  
  13. Turn off the air conditioning and reconnect all wires and hoses.
  14.  

ADJUSTMENTS FOR HOLLEY 6280



Fast Idle Cam Position

See Figure 45

  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  
  3. Insert a 0.07 in. (1.7mm) gauge between the upper edge of the choke plate and the wall.
  4.  



Click image to see an enlarged view

Fig. Fig. 45: Fast idle cam position adjusting

  1. If adjustment is necessary, bend the fast idle link at the angle until the specified gauge fits between the choke plate and the wall of the air horn.
  2.  

Vacuum Kick
  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 67 in. Hg (51 kPa).
  4.  
  5. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  6.  
  7. Insert a 0.13 in. (3.3mm) gauge between the choke valve and the wall of the air horn.
  8.  
  9. Remove the gauge. If a slight drag is not felt as the gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  10.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  

Choke Unloader

See Figure 46

  1. Hold the throttle valve in the wide-open position.
  2.  
  3. Insert a 0.25 in. (6.3mm) gauge between the upper edge of the choke valve and the wall of the air horn for carburetor model R-40132; or a 0.15 in. (3.8mm) gauge for all other carburetors.
  4.  



Click image to see an enlarged view

Fig. Fig. 46: Choke unloader adjustment

  1. While pressing lightly against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  2.  
  3. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  4.  

Accelerator Pump Stroke

See Figure 47

  1. Remove the bowl vent cover plate and vent valve lever spring. Be careful not to dislodge or lose the vent valve retainer.
  2.  
  3. Make sure that the pump connector rod is in the inner slot of the pump arm.
  4.  
  5. Position the throttle at curb idle, you can obtain the idle speed from the emissions label located in the engine compartment.
  6.  
  7. Place a straightedge on the bowl vent cover surface of the air horn over the accelerator pump connector rod in the center of the bowl.
  8.  



Click image to see an enlarged view

Fig. Fig. 47: Accelerator pump stroke measurement

  1. On 6585 models, bend the accelerator pump connector rod until the lever surface is flush with the air horn surface. On 6586-87 models, the lever surface should be 0.135 in. (3.4mm) above the casting.
  2.  
  3. Install the vent valve lever spring and bowl vent cover plate.
  4.  

If this adjustment is changed, both the bowl vent and the mechanical power valve adjustment must be reset.

Fast Idle Speed

See Figure 48

  1. Run the engine to normal operating temperature.
  2.  
  3. Disconnect and plug the EGR vacuum line and distributor advance vacuum line. Disconnect and plug the carburetor vacuum line at the heated air temperature sensor. Remove the air cleaner and plug the 3 / 16 in. (4.7mm) vacuum line at the charcoal canister. Remove the PCV valve from the rocker cover and allow it to draw fresh air.
  4.  
  5. Set the parking brake and place the transmission in Neutral.
  6.  



Click image to see an enlarged view

Fig. Fig. 48: Adjustment of fast idle speed

  1. With the engine off, open the throttle and place the fast idle adjusting screw on the second highest speed step of the cam.
  2.  
  3. Start the engine. Let the engine speed stabilize.
  4.  
  5. Turn the fast idle speed screw in or out until the engine speed listed on the underhood sticker is reached.
  6.  
  7. Reposition the screw on the cam after each adjustment in order to allow the idle to properly stabilize.
  8.  
  9. Reconnect the vacuum hoses and install the air cleaner.
  10.  

Float Setting

See Figure 49

  1. Remove the carburetor.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Remove the air horn.
  2.  
  3. Drain the float bowl of fuel.
  4.  
  5. Invert the carburetor body.
  6.  

The pump intake check ball will drop out. Be sure to catch it!

Click image to see an enlarged view

Fig. Fig. 49: Float setting adjustment

  1. Allow the weight of the floats to rest on the needle valve. Hold your finger against the hinge pin retainer to fully seat it in the float pin cradle.
  2.  
  3. Using a T-scale, measure the gap between the surface of the float bowl and the toe of each float. The gap should be 9 / 32 in. plus or minus 1 / 32 in.
  4.  
  5. If adjustment is necessary, bend the float tang. Bend either float arm to equalize the individual float positions.
  6.  

ADJUSTMENTS FOR ROCHESTER QUADRAJET



See Figure 50



Click image to see an enlarged view

Fig. Fig. 50: Rochester Quadrajet

Float Level External Check

See Figure 51

  1. With the engine idling at normal operating temperature and the choke wide-open, insert float gauge C-4900 in the vent hole. Allow the gauge to float freely.
  2.  


WARNING
Do not press down on the gauge, as this will result in flooding and/or float damage!



Click image to see an enlarged view

Fig. Fig. 51: Float level external check

  1. Look at the mark on the gauge that lines up with the top of the casting. The reading should be 13 / 32 in. plus or minus 1 / 16 in.
  2.  

Incorrect fuel pressure will result in a false reading. If this is suspected, test the fuel pump.

  1. If not, remove the air horn and set the float as described under Float Setting, later in this section.
  2.  

Float Setting

See Figure 52

  1. Remove the air horn, gasket, power piston, and the plastic float bowl insert.
  2.  
  3. Hold the float bowl retainer firmly in place.
  4.  
  5. Push the float down lightly against the needle.
  6.  



Click image to see an enlarged view

Fig. Fig. 52: Float adjustment

  1. Measure the float height from the top of the casting to the top of the float at a point 3 / 16 in. from the end of the float. The height should be 13 / 32 in. plus or minus 2 / 32 in.
  2.  
  3. If the float level is too high, hold the retainer in place and push down on the center of the float pontoon to get the correct setting.
  4.  
  5. If the float level is too low, bend the float upward to get the correct setting.
  6.  
  7. Recheck the float level.
  8.  
  9. Install the bowl insert, power piston and gasket, and air horn.
  10.  

Air Valve Spring

See Figure 53

  1. Using a 3 / 32 in. (2.3mm) wrench, loosen the air valve spring lockscrew.
  2.  
  3. Turn the tension adjusting screw counterclockwise until the air valve opens part way.
  4.  
  5. Turn the screw clockwise until the valve just closes.
  6.  



Click image to see an enlarged view

Fig. Fig. 53: Air valve spring adjustment

  1. Turn the screw clockwise for the following vender numbers, measured in turns:
  2.  



17085408- 1 / 2 turn
 
17085409- 5 / 8 turn
 
17085415- 1 / 2 turn
 
17085417- 3 / 4 turn
 
17086425- 1 / 2 turn
 
17087245- 5 / 8 turn
 
17087176- 3 / 4 turn
 
17087175- 3 / 4 turn
 
17087177-1 turn
 
17085431- 1 / 2 turn
 

  1. Hold the adjusting screw and tighten the locknut.
  2.  
  3. Apply a light film of lithium based grease to the contact area.
  4.  

Choke Coil Lever

See Figure 54

  1. Remove the choke cover.
  2.  
  3. Place the fast idle cam follower on the highest step of the cam.
  4.  
  5. Push up on the choke coil lever to close the choke plate.
  6.  



Click image to see an enlarged view

Fig. Fig. 54: Choke coil level adjustment

  1. Insert a 0.12 in. (3mm) plug gauge in the hole just below the choke coil lever. The lower edge of the lever should just contact the gauge.
  2.  
  3. If not, bend the choke rod at the upper angle.
  4.  

Fast Idle Cam

See Figure 55

  1. Attach a rubber band to the green tang of the intermediate choke shaft.
  2.  
  3. Open the throttle to allow the choke valve to close.
  4.  
  5. Place the cam follower on the second step of the cam. If the cam follower won't touch the cam, turn the fast idle speed screw in until it does.
  6.  



Click image to see an enlarged view

Fig. Fig. 55: Fast idle cam adjustment

  1. Apply a slight opening pressure on the choke blade and insert a 0.125 in. (3.1mm) plug gauge between the top of the choke blade and air horn casting.
  2.  
  3. If adjustment is needed, bend the tang of the fast idle cam until a slight drag is felt when the gauge is removed.
  4.  

Choke Vacuum Kick

See Figures 56 and 57

  1. Attach a rubber band to the green tang of the intermediate choke shaft.
  2.  
  3. Open the throttle to allow the choke valve to close.
  4.  



Click image to see an enlarged view

Fig. Fig. 56: Choke system

  1. Using a vacuum pump, apply at least 70 in. Hg (61 kPa) to the nipple on the choke diaphragm. The air valve rod must not restrict the plunger from fully retracting. If necessary, bend the rod to permit full plunger travel. The final rod clearance must be set after the vacuum kick setting has been made.
  2.  



Click image to see an enlarged view

Fig. Fig. 57: Choke vacuum kick adjustment

  1. With the vacuum still applied, apply a slight opening pressure on the choke plate and insert a 0.214 in. (5.4mm) gauge between the top of the choke plate and the air horn casting on all 6585 models, or a 0.17 in. (4.3mm) gauge on all 6586 models. On 6587-88 models, the gauge should be 0.150 in. (3.8mm) for 66 state models, 0.17 in. (4.3mm) for high altitude models, or 0.14 in. (3.5mm) for California and Canada models. A slight drag should be felt.
  2.  
  3. If adjustment is necessary, bend the link at the upper angle.
  4.  

Air Valve Rod

See Figure 58

  1. Using a vacuum pump, apply at least 70 in. Hg (61 kPa) to the vacuum nipple on the choke vacuum diaphragm.
  2.  
  3. Close the air valve.
  4.  



Click image to see an enlarged view

Fig. Fig. 58: Air valve rod adjustment

  1. Insert a 0.025 in. (0.6mm) gauge between the rod and the end of the slot. The gauge should just fit.
  2.  
  3. To adjust, bend the rod at the lower left angle.
  4.  

Choke Unloader

See Figure 59

  1. Attach a rubber band to the green tang of the intermediate choke shaft.
  2.  
  3. Open the throttle to allow the choke plate to close.
  4.  
  5. Hold the secondary lockout lever away from the pin.
  6.  
  7. Hold the throttle lever in the wide-open position.
  8.  



Click image to see an enlarged view

Fig. Fig. 59: Choke unloader adjustment

  1. Apply a slight opening pressure on the choke plate and insert a 0.345 in. (8.7mm) gauge between the top of the choke plate and the air horn wall for all 6585 models, or a 0.26 in. (6.6mm) gauge for all 6586 models. For 6587-88 models, use a 0.20 in. (5.0mm) gauge for 66 states models, 0.22 in. (5.5mm) for high altitude models; or a 0.209 in. (7.3mm) for California and Canada models. A slight drag should be felt.
  2.  
  3. If adjustment is required, bend the tang of the fast idle lever.
  4.  

Secondary Lockout
LOCKOUT LEVER

See Figure 60

  1. Close the choke plate.
  2.  
  3. Close the throttle plates.
  4.  



Click image to see an enlarged view

Fig. Fig. 60: Secondary lockout adjustment

  1. Insert a 0.015 in. (0.38mm) plug gauge between the lockout lever and the secondary throttle plate actuating pin. The gauge should just fit. If not, bend the pin.
  2.  

LOCKOUT OPENING CLEARANCE
  1. Hold the choke plate wide-open by pushing down on the tail of the fast idle cam.
  2.  
  3. Insert a 0.015 in. plug gauge between the end of the lockout lever and the end of the secondary throttle actuating pin. The gauge should just fit. If not, file the end of the pin.
  4.  

Fast Idle Speed
  1. Run the engine to normal operating temperature.
  2.  
  3. Disconnect and plug the EGR vacuum line and distributor advance vacuum line. Disconnect and plug the 3 / 16 in. vacuum hose at the charcoal canister. Remove the PCV valve from the rocker cover and allow it to draw fresh air.
  4.  
  5. Set the parking brake and place the transmission in Neutral.
  6.  
  7. With the engine off, open the throttle and place the fast idle adjusting screw on the second highest speed step of the cam.
  8.  
  9. Start the engine. Let the engine speed stabilize.
  10.  
  11. Turn the fast idle speed screw in or out until the engine speed listed on the underhood sticker is reached.
  12.  
  13. Reposition the screw on the cam after each adjustment in order to allow the idle to properly stabilize.
  14.  
  15. Reconnect the vacuum hoses and install the air cleaner.
  16.  

ADJUSTMENTS FOR STROMBERG WW3



Float Height

See Figure 61

  1. Remove the carburetor.
  2.  

Position the carburetor on clean rags to catch any remaining fuel.

  1. Remove the air horn.
  2.  
  3. Drain the float bowl of fuel.
  4.  
  5. Invert the main body and let the weight of the float rest on the needle and seat.
  6.  
  7. Using a T-scale, check the distance between the gasket surface of the fuel bowl (gasket removed) and the top of the float at the center. The gap should be 7 / 32 in. (5.5mm).
  8.  



Click image to see an enlarged view

Fig. Fig. 61: Float settings

  1. If adjustment is necessary, hold the float against the bottom of the float bowl and bend the lip towards or away from the needle.
  2.  


WARNING
When bending, don't allow the float lip to push against the needle. The tip of the needle will compress and give a false reading.

  1. Recheck your adjustment a couple of times. It is very important that the float lip be perpendicular to the needle within 10° after the adjustment!
  2.  
  3. Assemble and install the carburetor.
  4.  

Fast Idle Cam
  1. Position the fast idle speed adjusting screw so that it contacts the second highest step of the cam. Move the choke valve toward the closed position using light pressure on the choke linkage.
  2.  
  3. Insert a 0.08 in. (2.25mm) gauge between the upper edge of the choke plate and the wall of the air horn on all engines except the 8-318 with the Clean Air Package. On these engines, use a 0.16 in. (4.1mm) gauge bit. A slight drag should be felt.
  4.  

  1. If adjustment is necessary, bend the fast idle link at the upper angle until the specified gauge fits between the choke plate and the wall of the air horn.
  2.  

Vacuum Kick
  1. If the adjustment is to be made on the engine (with the engine running at curb idle), back off the fast idle screw until the choke can be closed to the kick position. Note the number of screw turns required so that the fast idle can be returned to the original adjustment.
  2.  
  3. If the adjustment is to be made off the engine, open the throttle valve and move the choke to its closed position. Release the throttle first and then release the choke. Disconnect the vacuum hose from the carburetor body and apply a vacuum of at least 10 in. Hg (34 kPa).
  4.  
  5. Insert a 0.21 in. (5.4mm) gauge between the choke valve and the wall of the air horn.
  6.  
  7. Apply sufficient closing pressure to the choke lever to provide a minimum valve opening without distorting the diaphragm link (which connects the choke lever to the vacuum diaphragm). Note that the cylindrical stem of the diaphragm will extend as its internal spring is compressed. This spring must be fully compressed for the proper measurement of the vacuum kick adjustment.
  8.  
  9. Remove the gauge bit. If a slight drag is not felt as the gauge is removed, an adjustment of the diaphragm link is necessary to obtain the proper clearance. Shorten or lengthen the diaphragm link by carefully closing or opening the U-bend in the link until the correct adjustment is obtained.
  10.  


WARNING
When adjusting the link, be careful not to bend or twist the diaphragm.

  1. Connect the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
  2.  
  3. With no vacuum applied to the diaphragm, the choke valve should move freely between its open and closed positions. If it does not move freely, examine the linkage for misalignment or interference which may have been caused by the bending operation. If necessary, repeat the adjustment to provide the proper link operation.
  4.  

Choke Unloader
  1. Hold the throttle valve in the wide-open position.
  2.  
  3. Insert a 5 / 16 in. (7.9mm) gauge between the upper edge of the choke valve and the wall of the air horn.
  4.  
  5. While pressing lightly against the choke lever, a slight drag should be felt as the gauge is being withdrawn.
  6.  
  7. If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
  8.  

Accelerator Pump and Bowl Vent
  1. Back off the idle speed adjusting screw.
  2.  
  3. Open the choke plate so that, with the throttle plates closed, the fast idle adjusting screw will not contact the fast idle cam.
  4.  
  5. Make sure that the pump rod is in the medium stroke hole in the throttle lever and the bowl vent clip on the pump stem is in the center notch.
  6.  
  7. Close the throttle plates tightly. It should be just possible to insert a 0.06 in. (0.15mm) gauge between the bowl vent and the vent seal. Engine equipped with the Clean Air Package use a 0.05 in. (1.2mm) gauge.
  8.  
  9. If adjustment is necessary, bend the pump rod at the lower angle with needle-nosed pliers.
  10.  

Fast Idle Speed
  1. Run the engine until it reaches normal operating temperature.
  2.  
  3. With the engine off and the transmission in Park or Neutral, open the throttle slightly.
  4.  
  5. On models without the Clean Air Package, close the choke plate about 20°, then allow the throttle plates to close. The fast idle screw should now rest on the slowest speed step of the cam. On models with the Clean Air Package, close the choke plate until the fast idle screw can be positioned on the second highest speed step of the cam.
  6.  
  7. Start the engine.
  8.  
  9. Turn the fast idle speed screw in or out until 700 rpm is obtained.
  10.  
  11. Stopping the engine between adjustments is not necessary. However, be sure the fast idle speed screw is positioned on the cam after each speed adjustment.
  12.  

REMOVAL & INSTALLATION



See Figures 62 through 70


CAUTION
Do not attempt to remove a carburetor from a vehicle that has just been road tested. The truck MUST BE completely cooled down before working on it. The possibility of fuel igniting and severe personal injury exists. ALWAYS observe "no smoking/no open flame'' precautions.

The following is general removal procedure for all carburetors.

  1. Disconnect the battery ground cable.
  2.  
  3. Remove the air cleaner.
  4.  



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Fig. Fig. 62: The air cleaner must be removed for access to the carburetor



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Fig. Fig. 63: Note the positions and routing of all carburetor linkage

  1. Remove the fuel tank filler cap. The tank could be under a small amount of pressure.
  2.  
  3. Tag all lines to the carburetor before removing them, this is important, so there is no confusion.
  4.  



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Fig. Fig. 64: Vacuum lines need to be inspected and replaced if bad on installation



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Fig. Fig. 65: Tag all lines before disconnecting them from the carburetor

  1. Disconnect and plug the fuel lines. Use two wrenches to avoid twisting the fuel line. A container is also useful to catch any fuel which spills from the lines.
  2.  



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Fig. Fig. 66: Use two wrenches on fuel fittings to avoid twisting and breaking a line

  1. Disconnect the throttle and choke linkage along with any springs.
  2.  



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Fig. Fig. 67: The throttle linkage needs to be disconnected and removed



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Fig. Fig. 68: Remove the springs and inspect them for wear or damage

  1. Disconnect any vacuum lines.
  2.  
  3. Remove the mounting bolts.
  4.  
  5. Make sure all connections are disconnected. Carefully remove the carburetor from the engine and carry it in a level position to a clean work place.
  6.  



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Fig. Fig. 69: Make sure all components are disengaged, then remove the carburetor and place it on a clean work surface

Position the carburetor on clean rags to catch any remaining fuel.

  1. Remove the gasket and or insulator assembly. Clean the surface of the intake manifold and bottom of the carburetor. Always install the carburetor with a new insulator and gasket to prevent leaks.
  2.  



Click image to see an enlarged view

Fig. Fig. 70: Remove the carburetor insulator assembly

While the carburetor is removed, cover the openings in the intake manifold to prevent the entrance of dirt or foreign matter.

To install:
  1. Place a new gasket on the manifold.
  2.  
  3. Carefully place the carburetor on the manifold without trapping the choke rod under carburetor linkage.
  4.  
  5. Install the carburetor mounting nuts and or bolts making sure to tighten alternately, a little at a time. This will compress the gasket evenly, and help prevent vacuum leakage between the carburetor and the manifold.
  6.  
  7. Connect the throttle linkage and the fuel inlet line.
  8.  
  9. Check for worn or loose vacuum hose connections. Look at your vacuum diagram label under the hood of your truck for correct placement.
  10.  
  11. Make sure the choke plate opens and closes completely when operated. Also check to see if throttle travel is not hindered.
  12.  
  13. Install the air cleaner. It is always a good idea to clean and inspect it before installation.
  14.  
  15. Connect the battery cable.
  16.  
  17. Check the idle mixture and speed adjustments.
  18.  


CAUTION
The practice of priming an engine by pouring gasoline into the carburetor air horn, should be strictly avoided. Cranking the engine, then priming by depressing the accelerator peel several times, should be adequate.

OVERHAUL



Efficient carburetion depends greatly on careful cleaning and inspection during overhaul since dirt, gum, water or varnish in or on the carburetor parts are often responsible for poor performance.

Overhaul the carburetor in a clean, dust free area. Carefully disassembly the carburetor, referring often to the exploded views. Keep all similar and look-alike parts segregated during disassembly and cleaning to avoid accidental interchange during assembly. Make a note of all jet sizes.

When the carburetor is disassembled, wash all parts (except diaphragms, electric choke units, pump plunger and any other plastic, leather, fiber, or rubber parts) in clean carburetor solvent. Do not leave the parts in the solvent any longer than is necessary to sufficiently loosen the dirt and deposits. Excessive cleaning may remove the special finish from the float bowl and choke valve bodies, leaving these parts unfit for service. Rinse all parts in clean solvent and blow them dry with compressed air or allow them to air dry, while resting on clean, lint-free paper. Wipe clean all cork, plastic, leather and fiber parts with clean, lint free cloth.

Blow out all passages and jets with compressed air and be sure that there are no restrictions or blockages. Never use wire or similar tools to clean jets, fuel passages or air bleeds. Clean all jets and valves separately to avoid accidental interchange.

Examine all parts for wear or damage. If wear or damage is found, replace the defective parts. Especially, inspect the following:

  1. Check the float needle and seat for wear. If wear is found, replace the complete assembly.
  2.  
  3. Check the float hinge pin for wear and the float(s) for dents or distortion. replace the float if fuel has leaked into it.
  4.  
  5. Check the throttle and choke shaft bores for wear or an out-of-round condition. Damage or wear to the throttle arm, shaft or shaft bore will often require replacement of the throttle body. These parts require a close tolerance of fit; wear may allow air leakage, which could affect starting and idling.
  6.  

Throttle shaft and bushings are not normally included in overhaul kits. They may be available separately for purchase.

  1. Inspect the idle mixture adjusting needles for burrs and grooves. Any such condition requires replacement of the needle, since you will not be able to obtain a satisfactory idle.
  2.  
  3. Test the accelerator pump check valves. They should pass air one way, but not the other. Test for proper seating by blowing and sucking on the valve. Replace the valve as necessary. If the valve is satisfactory, wash the valve again to remove moisture.
  4.  
  5. Check the bowl cover for warped surfaces with a straightedge.
  6.  
  7. Closely inspect the valves and seats for wear and damage, replacing as necessary.
  8.  
  9. After the carburetor is assembled, check the choke valve for freedom of operation.
  10.  

Carburetor overhaul kits are recommended for each overhaul. these kits contain all gaskets and new parts to replace those which deteriorate most rapidly. Failure to replace all of the parts supplied with the kit (especially gaskets) can result in poor performance later.

Most carburetor manufacturers supply overhaul kits of three basic types: minor repair; major repair; and gasket kits. Basically, they contain the following:

Minor Repair Kits:


All gaskets
 
Float needle valve
 
All diagrams
 
Spring for the pump diaphragm
 

Major Repair Kits:


All jets and gaskets
 
All diaphragms
 
Float needle valve
 
Pump ball valve
 
Float
 
Complete intermediate rod
 
Intermediate pump lever
 
Some cover hold-down screws and washers
 

Gasket kits:


All gaskets
 

After cleaning and checking all components, reassemble the carburetor, using new parts and referring to the exploded view. When reassembling, make sure that all screws and jets are right in their seat, but do not overtighten, as the tip will be distorted. Tighten all screws gradually, in rotation. Do not tighten needle valves into their seats; uneven jetting will result. Always use new gaskets. Be sure to adjust the float level.

Most carburetor rebuilding kits contain a sheet of specific instructions pertaining to the carburetor the kit is for.

 
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