- Back off the idle speed screw.
- Make sure that the pump connector rod is in the center hole of the throttle lever.
- Close the throttle valves tightly. It should just be possible to insert a 1 / 64 " drill bit between the top of the air horn and the end of the plunger shaft.
- If an adjustment is necessary, bend the pump operating rod at the lower angle.
- Reset the idle.
See Figure 1
- Back off the idle speed screw to completely close the throttle plate.
- Open the choke plate so that the fast idle cam allows the throttle plates to seat in their bores.
- Make sure that the accelerator pump S-link is in the outer hole of the pump arm.
- Turn the curb idle adjusting screw clockwise until it just contacts the stop, then, turn it 2 full turns more.
- Measure the distance between the surface of the air horn and the top of the accelerator pump shaft. The gap should be 1 / 2 ".
- To adjust the pump travel, loosen the pump arm adjusting lockscrew and rotate the sleeve until the proper gap is reached.
AUTOMATIC CHOKE ONLY
See Figure 2
- Adjust the fast idle speed as described later.
- Place the fast idle screw on the second highest step of the fast idle cam.
- Move the choke valve towards the closed position with light pressure on the choke shaft lever.
- Insert a #48 drill bit between the choke valve and the wall of the air horn on models through 1972. On 1973-84 models use a 0.110" drill bit on carb. models 8147S; an 0.070" drill bit on all other models. If an adjustment is necessary, bend the fast idle rod at the upper angle.
See Figure 3
- 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.
- 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 (15 in.Hg for 1976 and later models).
- Insert a #35 drill bit between the choke valve and the wall of the air horn on models through 1972. On models through 1979, use a 0.110" drill bit. On models through 1981, use a 0.070" drill bit on models 8146S or 0.150" on models 8147S. On models through 1984 use a 0.070" drill bit on model 8146S, 0.150" drill bit on model 8147S, and 0.130" on all others.
- 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.
- Remove the drill bit. If a slight drag is not felt as the drill bit 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.
- Refit the vacuum hose to the carburetor body (if it had been removed) and return the fast idle screw to its original location.
- 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.
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:
- Hold the throttle valve in the wide open position.
- Insert a 3 / 16 " drill bit between the upper edge of the choke valve and the wall of the air horn on models through 1972. On 1973-79 models, use a 0.280" drill bit. On 1980-81 models, use a 0.310" drill bit. On 1982-84 models use a 0.310" drill bit for carb.# 8146S and 8147S, and 0.280" for all others.
- With a finger pressing lightly against the choke plate, a slight drag should be felt as the drill is being withdrawn.
- If adjustment is necessary, bend the unloader tang on the throttle lever until the correct opening is obtained.
See Figure 5
- Hold the throttle plates closed. It should be possible to insert a 0.060" drill bit between the bowl vent valve and the air horn on models through 1979; 0.080" on 1980-84 models.
- If adjustment is necessary, bend the short tang on the vent operating lever until the proper clearance is reached.
See Figure 6
This procedure is performed with the carburetor on the engine.
- Remove the clips and disengage the accelerator pump operating rod from the throttle lever and the pump rocker arm.
- Remove the air horn attachment screws and lift the air horn straight up, and away from the main body. Remove the gasket.
- 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.
- 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 1972, the gap should be 15 / 64 " on models with a manual choke; 5 / 16 " on models with an automatic choke. On later models, the gap should be 1 / 4 ".
- 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.
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+-10°.
- Assemble the air horn.
- Check the idle speed.
See Figure 7
- Warm the engine by driving at least five miles.
- With the engine off and the transmission in Park or Neutral, open the throttle slightly.
- 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.
- Start the engine.
- On trucks through 1972, turn the fast idle speed screw in or out until 1,700 rpm is obtained for carb. model 6536S; 1,500 rpm for all other models.
On 1973-84 models, check your underhood sticker for the proper speed.
- Stopping the engine between adjustments is not necessary. However, be sure to position the fast idle speed screw on the cam after each speed adjustment.