GM Full Size Vans 1967-1986 Repair Guide

Carburetor

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PRELIMINARY CHECKS



All Models

The following should be observed before attempting any adjustments.

  1. Thoroughly warm the engine. If the engine is cold, be sure that it reaches operating temperature.
  2.  
  3. Check the torque of all carburetor mounting nuts. Also check the intake manifold-to-cylinder head bolts. If air is leaking at any of these points, any attempts at adjustment will inevitably lead to frustration.
  4.  
  5. Check the manifold heat control valve (if used) to be sure that it is free.
  6.  
  7. Check and adjust the choke as necessary.
  8.  
  9. Adjust the idle speed and mixture. If any adjustments are performed that might possibly change the idle speed or mixture, adjust the idle and mixture again when you are finished.
  10.  

ADJUSTMENTS



These adjustment are arranged by carburetor model. Most of these vans use General Motors Rochester carburetors. The first number of the carburetor model number indicates the number of barrels, while the last letter indicates the type of choke used. These are V for the manifold mounted choke coil, C for the choke coil mounted on the carburetor, and E for electric choke.

Most of these adjustments require that measurements be made to thousandths of an inch, using some sort of gauge. Drill bits are ideal for this purpose.

Rochester B Carburetor-1967 Models
FLOAT LEVEL AND FLOAT DROP

See Figures 1 and 2



Click image to see an enlarged view

Fig. Fig. 1: View of the Rochester B float level adjustment



Click image to see an enlarged view

Fig. Fig. 2: View of the Rochester B float drop adjustment

The air horn must be removed to make this adjustment. The carburetor need not be removed from the manifold.

  1. Remove the air cleaner and the air horn.
  2.  
  3. Hold the air horn (with the gasket in place) so that the floats hang free.
  4.  
  5. Measure the distance from the gasket surface to the bottom of the float with a T-scale. The distance should be as specified. If not, bend the tang until the floats are parallel and the specified distance from the gasket. The floats should also be aligned to avoid interference with the bowl.
  6.  
  7. Turn the air horn over so that the float arm closes the needle valve. Bend the tang until the distance is as specified.
  8.  
  9. Reinstall the air horn and adjust the idle speed and mixture.
  10.  

IDLE VENT
  1. Open the throttle and insert the specified gauge between the throttle valve and the bore opposite the idle needle.
  2.  
  3. Adjust by turning the valve on top of the air horn until the vent is just opening.
  4.  

Carter YF Carburetor-1967 Models

See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: Exploded view of a Carter YF carburetor

IDLE VENT
  1. With choke open, back out the idle speed screw until free to close the throttle valve.
  2.  
  3. Insert feeler gauge between the air horn and vent valve. Adjust to get 0.065 in. (1.651mm) clearance.
  4.  

FAST IDLE AND CHOKE VALVE
  1. Hold the choke valve closed.
  2.  
  3. Close the throttle and mark the position of the throttle lever tang on the fast idle cam.
  4.  
  5. The mark on the fast idle cam should align with the upper edge of the tang on the throttle lever. If not, bend the choke rod as necessary.
  6.  

CHOKE UNLOADER
  1. Open the throttle to the wide open position.
  2.  
  3. Using a rubber band, hold the choke valve closed.
  4.  
  5. Bend the unloader tang on the throttle lever to get the proper clearance between the lower edge of the choke valve and the air horn wall.
  6.  

VACUUM BREAK
  1. Hold the vacuum break arm against its stop and hold the choke closed with a rubber band.
  2.  
  3. Bend the vacuum bread link to get the specified distance between the lower edge of the choke valve and the air horn wall.
  4.  

FLOAT LEVEL
  1. Turn the bowl cover upside down and measure the float level by measuring the distance between the float (free end) and the cover. The distance should be 7 / 32 in. (5.5mm); if not bend the lip of the float, not the float arm.
  2.  
  3. Hold the cover in proper position (not upside down) and measure the amount of float drop from the cover to the float bottom at the end opposite the hinge. This distance should be specified.
  4.  
  5. Make the adjustment by the stop tab on the float arm.
  6.  

ACCELERATOR PUMP
  1. Seat the throttle valve by backing off the idle speed screw.
  2.  
  3. Hold the throttle valve closed.
  4.  
  5. Fully depress the diaphragm shaft and check the contact between lower retainer and the lifter link.
  6.  
  7. This retainer (upper pump spring) should just contact the pump lifter link buy do not compress the spring.
  8.  
  9. To adjust bend the pump connector link at its U-bend.
  10.  

METERING ROD
  1. Insert the metering rod through the metering jet and close the throttle valve. Press down on the upper pump spring until the pump bottoms.
  2.  
  3. Metering rod arm must rest on the pump lifter link and the rod eye should just slide over the arm pin.
  4.  
  5. To adjust, bend the metering rod arm.
  6.  

Rochester M and MV Carburetors-1968-74 Models

FAST IDLE SPEED

The fast idle adjustment must be made with the transmission in Neutral.

  1. Position the fast idle lever on the high step of the fast idle cam.
  2.  
  3. Be sure that the choke is properly adjusted and in the wide open position with the engine warm.
  4.  
  5. Bend the fast idle lever until the specified speed is obtained.
  6.  

CHOKE ROD (FAST IDLE CAM)

Adjust the fast idle before making choke rod adjustments.

  1. Place the fast idle cam follower on the second step of the fast idle cam and hold it firmly against the rise to the high step.
  2.  
  3. Rotate the choke valve in the direction of a closed choke by applying force to the choke coil lever.
  4.  
  5. Bend the choke rod, at the lower angle, to give the specified opening between the lower edge of the choke valve and the inside air horn wall.
  6.  

Measurement must be made at the center of the choke valve.

CHOKE VACUUM BREAK

The adjustment of the vacuum break diaphragm unit insures correct choke valve opening after engine starting.

  1. Remove the air cleaner on vehicles with Therm/AC air cleaner; plug the sensor's vacuum take off port.
  2.  
  3. Using an external vacuum source, apply vacuum to the vacuum break diaphragm until the plunger is seated, push the choke valve toward the closed position. The vacuum break rod should be in the end of the slot.
  4.  
  5. Holding the choke valve in this position, place the specified gauge between the lower edge of the choke valve and the air horn wall.
  6.  
  7. If the measurement is not correct, bend the vacuum break rod at the angle.
  8.  

CHOKE UNLOADER
  1. Apply pressure to the choke valve and hold it in the closed position.
  2.  
  3. Open the throttle valve to the wide open position.
  4.  
  5. Check the dimension between the lower edge of the choke plate and the air horn wall; if adjustment is needed, bend the unloader tang on the throttle lever to adjust to specification.
  6.  

AUTOMATIC CHOKE COIL ROD
  1. Disconnect the coil rod from the upper choke lever and hold the choke valve closed.
  2.  
  3. Push down on the coil rod to the end of its travel.
  4.  
  5. The top of the rod should be even with the bottom hole in the choke lever.
  6.  
  7. To make adjustments, bend the rod at the center.
  8.  

FLOAT LEVEL
  1. Remove the carburetor top. Hold the float retainer in place and the float arm against the top of the float needle by pushing down on the flat arm at the outer end toward the flat bowl casting.
  2.  
  3. Using an adjustable T scale, measure the distance from the tow of the float to the float bowl gasket surface.
  4.  

The float bowl gasket should be removed and the gauge held on the index point on the float for accurate measurement.

  1. Adjust the float level by bending the float arm up or down at the float arm junction.
  2.  

METERING ROD
  1. Hold the throttle valve wide-open and push down on the metering rod against spring tension, then remove the rod from the main metering jet.
  2.  
  3. In order to check adjustment, the slow idle screw must be backed out and the fast idle cam rotated so that the fast idle cam follower does not contact the steps on the cam.
  4.  
  5. With the throttle valve closed, push down on the power piston until it contacts its stop.
  6.  
  7. With the power piston depressed, swing the metering rod holder over the flat surface of the bowl casting next to the carburetor bore.
  8.  
  9. Insert a specified size drill between the bowl casting sealing beak and the lower surface of the metering rod holder. The drill should slide smoothly between both surfaces.
  10.  
  11. If adjustment is needed, carefully bend the metering rod holder up or down at the point shown. After adjustment, reinstall the metering rod.
  12.  

IDLE VENT-1968-69 MODELS
  1. The engine idle must be set at the specified rpm and the choke valve held wide-open so that the fast idle cam follower is not contacting the cam.
  2.  

If the carburetor is off the car, a preliminary idle setting can be made by turning the idle speed screw in 11/2turns from the closed throttle valve position.

  1. With the throttle stop screw held against the idle stop screw, the idle vent valve should be open 0.050 in. (1.27mm). To check, a drill of specified size may be inserted between the top of the air horn casting and the bottom surface of the valve.
  2.  
  3. If adjustment is necessary, turn the slotted vent valve head with a screwdriver. Turning the head clockwise increases the clearance.
  4.  

On models equipped with an idle stop solenoid, the solenoid must be activated when checking and adjusting the valve.

COMBINED EMISSION CONTROL (CEC) SOLENOID-1971-73 MODELS

Do not use the CEC valve to set idle rpm.

  1. With the engine running, and transmission in Neutral (manual) or Drive (automatic), air conditioner OFF, distributor vacuum hose removed and plugged, and fuel tank vapor hose disconnected, manually extend the CEC valve plunger to contact the throttle lever.
  2.  
  3. Adjust the plunger length to obtain the CEC valve rpm.
  4.  
  5. Reconnect the vapor hose and vacuum hose.
  6.  

Model 1MV and 1ME Carburetors-1975-78 Models

FAST IDLE SPEED

See Figure 4

Click image to see an enlarged view

Fig. Fig. 4: Location of the cam follower and the tang for the fast idle adjustment-1MV and 1ME carburetors

  1. Check and adjust the idle speed.
  2.  
  3. With the engine at normal operating temperature, air cleaner ON, EGR valve signal line disconnected and plugged and the air conditioning OFF, connect a tachometer.
  4.  
  5. Disconnect the vacuum advance hose at the distributor and plug the line.
  6.  
  7. With the transmission in Neutral (park on automatic), start the engine and set the fast idle cam follower on the high step of the cam.
  8.  
  9. Bend the tang in or out to obtain the fast idle speed.
  10.  

FAST IDLE CAM (CHOKE ROD)
  1. Check and adjust the fast idle speed.
  2.  
  3. Set the fast idle cam follower on the second step of the cam.
  4.  
  5. Apply force to the choke coil rod to hold the choke valve toward the closed position.
  6.  
  7. Measure the clearance between the upper edge (lower 1975) of the choke valve and the inside of the air horn wall.
  8.  
  9. Bend the rod at the lower angle to adjust.
  10.  

CHOKE UNLOADER
  1. Hold the choke valve down by applying light force to the choke coil lever.
  2.  
  3. Open the throttle valve to wide open.
  4.  
  5. Measure the clearance between the upper edge of the choke valve and the air horn wall.
  6.  
  7. If adjustment is necessary, bend the tang on the throttle lever.
  8.  

FLOAT LEVEL

The adjustment is the same as that for the Model MV carburetor, which appears earlier in this section.

AUTOMATIC CHOKE COIL ROD-1975 MODELS
  1. Detach the top of the rod. Pull the rod up to the end of its travel. Completely close the choke valve.
  2.  
  3. The bottom of the rod should be even with the top of the lever.
  4.  
  5. If adjustment is necessary, bend the rod.
  6.  

AUTOMATIC CHOKE COIL ROD-1976 MODELS
  1. Detach the top of the rod. Completely close the choke valve. Push the rod down to the end of its travel.
  2.  
  3. The top of the rod should be even with the bottom of the hole in the choke lever.
  4.  
  5. Bend the rod to adjust.
  6.  

ELECTRIC CHOKE ADJUSTMENT-1977-78 1ME MODELS
  1. Place the cam follower on the highest step of the fast idle cam.
  2.  
  3. Hold the choke valve completely closed.
  4.  
  5. Insert a 0.120 in. (3mm) drill bit through the hole in the end of the choke coil housing lever. It should go into the hole in the casting at about the 11 o'clock position.
  6.  
  7. Bend the choke coil rod to adjust.
  8.  
  9. Loosen the three retaining screws and set the choke coil pointer to the center index mark.
  10.  

Failure of the electric choke heater circuit will cause the oil pressure light to go on.

PRIMARY VACUUM BREAK-1975 MODELS
  1. With an outside vacuum source, apply vacuum to the primary vacuum break diaphragm until the plunger is fully seated. The primary diaphragm is the one on the opposite side from the idle speed solenoid.
  2.  
  3. Measure the clearance between the lower edge of the choke valve and the air horn wall.
  4.  
  5. Bend the vacuum break rod to adjust the clearance. Be sure there is no binding or interference.
  6.  

PRIMARY VACUUM BREAK-1976-77 MODELS
  1. Place the cam follower on the highest step of the fast idle cam.
  2.  
  3. Tape over the diaphragm housing bleed hole.
  4.  
  5. Apply vacuum until the plunger seats.
  6.  
  7. Push up on the choke coil lever rod in the end of the slot.
  8.  
  9. Measure between the upper end of the choke valve and the air horn. Bend the rod to adjust.
  10.  

AUXILIARY VACUUM BREAK-1975 MODELS
  1. With the outside vacuum source, apply vacuum to the auxiliary vacuum break diaphragm (on the same side of the carburetor as the idle speed solenoid) until the plunger seats.
  2.  
  3. Place the cam follower on the high step of the fast idle cam.
  4.  
  5. Measure the clearance between the upper edge of the choke valve and the air horn wall. Bend the link between the vacuum break and the choke valve to adjust.
  6.  

Rochester 2G and 2GV Carburetors-1967-74 Models

These procedures are for both the 1 1 / 4 in. (31.75mm) and 1 1 / 2 in. (38.1mm) models. Where there are differences these are noted. The 1 1 / 4 in. model has larger throttle bores and an additional fuel feed circuit to make it suitable for use on the 350 V8.

FAST IDLE CAM (CHOKE ROD)
  1. Turn the idle screw onto the second step of the fast idle cam, abutting against the top step.
  2.  
  3. Hold the choke valve toward the closed position and check the clearance between the upper edge of the choke valve and the air horn wall.
  4.  
  5. If this measurement varies from specifications, bend the tang on the choke lever.
  6.  

CHOKE VACUUM BREAK
  1. Apply vacuum to the diaphragm to fully seat the plunger.
  2.  
  3. Push the choke valve in toward the closed position and hold it there.
  4.  
  5. Check the distance between the lower edge of the choke valve and the air horn wall.
  6.  
  7. If this dimension is not within specifications, bend the vacuum break rod to adjust.
  8.  

CHOKE UNLOADER
  1. Hold the throttle valves wide-open and use a rubber band to hold the choke valve toward the closed position.
  2.  
  3. Measure the distance between the upper edge of the choke valve and the air horn wall.
  4.  
  5. If this measurement is not within specifications, bend the unloader tang on the throttle lever to correct it.
  6.  

AUTOMATIC CHOKE COIL ROD
  1. Hold the choke valve completely open.
  2.  
  3. With the choke coil rod disconnected from the upper level, push downward on the end of the rod to the end of its travel.
  4.  
  5. With the rod pushed fully downward, the bottom of the rod should be even with the bottom of the slotted hole in the lever.
  6.  
  7. To adjust the lever, bend it by using a screwdriver in the smaller slot.
  8.  

ACCELERATOR PUMP ROD
  1. Back the idle stop screw out and close the throttle valves in their bores.
  2.  
  3. Measure the distance from the top of the air horn to the top of the pump rod.
  4.  
  5. Bend the pump rod at a lower angle to correct this dimension.
  6.  

FLOAT LEVEL

Invert the air horn, and with the gasket in place and the needle seated, measure the level as follows:



On nitrophyl floats, measure from the air horn gasket to the lip on the toe of the float.
 
On brass floats, measure from the air horn gasket to the lower edge of the float seam.
 

Bend the float tang to adjust the level.

FLOAT DROP

Holding the air horn right side up, measure float drop as follows:



On nitrophyl floats, measure from the air horn gasket to the lip at the toe of the float.
 
On brass floats, measure from the air horn gasket to the bottom of the float.
 

Bend the float tang to adjust either type floats.

Model 2GC Carburetor-1975-78 Models
ACCELERATOR PUMP ROD
  1. Back out the idle speed adjusting screw.
  2.  
  3. Hold the throttle valve completely closed.
  4.  
  5. Measure the distance from the top of the air horn ring to the top of the pump rod.
  6.  
  7. If necessary, bend the pump rod to adjust.
  8.  

FAST IDLE CAM
  1. Place the idle speed screw on the second step of the fast idle cam against the highest step.
  2.  
  3. Measure the clearance between the upper edge of the choke valve and the air horn wall.
  4.  
  5. Bend the choke lever tang to adjust.
  6.  

CHOKE UNLOADER
  1. With the throttle valves wide open, place the choke valve in the closed position.
  2.  
  3. Measure the clearance between the upper edge of the choke valve and the air horn casting.
  4.  
  5. Bend the throttle lever tang to adjust.
  6.  

INTERMEDIATE CHOKE ROD
  1. Remove the thermostatic cover coil, gasket, and inside baffle plate.
  2.  
  3. Place the idle screw on the high step of the fast idle cam.
  4.  
  5. Close the choke valve by pushing up on the intermediate choke lever.
  6.  
  7. Insert a 0.120 in. (3mm) drill bit into the hole inside the choke housing (at about the 11 o'clock position). The edge of the choke lever must align with the edge of the bit.
  8.  
  9. Bend the intermediate choke rod between the two upper bends to adjust.
  10.  

AUTOMATIC CHOKE COIL
  1. Place the idle screw on the high step of the fast idle cam.
  2.  
  3. Loosen the thermostatic choke coil cover retaining screws.
  4.  
  5. Rotate the choke cover against coil tension until the choke valve begins to close. Continue rotating it until the index mark aligns with the specified point on the choke housing. This point is centered (index), except for 1975-76 automatic, which is one notch rich.
  6.  
  7. Tighten the choke cover retaining screws.
  8.  

CHOKE VACUUM BREAK
  1. Disconnect the vacuum hose. Using an outside vacuum source, seat the vacuum diaphragm.
  2.  
  3. Cover the vacuum break bleed hole with a small piece of tape so that the diaphragm will be hold inward.
  4.  
  5. Place the idle speed screw on the high step of the fast idle cam.
  6.  
  7. Hold the choke coil lever inside the choke housing toward the closed choke position.
  8.  
  9. Measure the clearance between the upper edge of the choke valve and the air horn wall.
  10.  
  11. Bend the vacuum break rod to adjust.
  12.  
  13. After adjustment, remove the piece of tape and reconnect the vacuum hose.
  14.  

FLOAT LEVEL AND FLOAT DROP

These procedures are the same as for the model 2GV, covered earlier.

Rochester 2SE Carburetor-1979-84 Models

See Figures 5 and 6



Click image to see an enlarged view

Fig. Fig. 5: Exploded view of the Rochester 2SE carburetor (key list appears on next page)



Click image to see an enlarged view

Fig. Fig. 6: Rochester 2SE carburetor key list

FLOAT ADJUSTMENT
  1. Hold the float retainer in place with you hand and push the float down against the needle.
  2.  
  3. Place a 1 / 8 in. (3mm) gauge at the toe of the float, as illustrated.
  4.  
  5. Remove the float and bend the arm as necessary to adjust the level.
  6.  

FAST IDLE ADJUSTMENT
  1. Refer to the underhood emissions sticker. Disconnect and plug any hoses indicted on the sticker.
  2.  
  3. Adjust the curb idle speed as outlined in Engine Electrical .
  4.  
  5. Place the fast idle screw on the high step of the fast idle cam.
  6.  
  7. Turn the screw in or out to adjust the fast idle speed.
  8.  

CHOKE COIL LEVER ADJUSTMENT

Refer to the illustration for this adjustment.

ELECTRIC CHOKE SETTING
  1. Loosen the three choke coil retaining screws.
  2.  
  3. Place the fast idle screw on the high step of the fast idle adjusting cam.
  4.  
  5. Set the line on the choke 1 notch counterclockwise from the center mark.
  6.  

AIR VALVE ROD ADJUSTMENT
  1. Fully seat the diaphragm using an outside vacuum source.
  2.  
  3. Be sure the air valve is completely closed.
  4.  
  5. Place a 0.040 in. (1mm) gauge between the rod and the end of the slot in the lever.
  6.  
  7. Bend the rod to obtain 0.040 in. (1mm) clearance.
  8.  

FAST IDLE CAM CHOKE ROD ADJUSTMENT
  1. The choke coil lever and the fast idle adjustments must be correct before performing this adjustment.
  2.  
  3. Install a special choke valve measuring gauge (no. J-26701) on the carburetor.
  4.  
  5. Rotate the degree scale until the zero mark is opposite the pointer.
  6.  
  7. With the choke valve completely open, place the magnet directly on top of the choke valve.
  8.  
  9. Rotate the bubble until it is centered.
  10.  
  11. Rotate the scale to place the 17° mark opposite the pointer.
  12.  
  13. Place the fast idle screw on the second highest step of the fast idle cam.
  14.  
  15. Close the choke by pushing on the intermediate choke lever.
  16.  
  17. Push on the vacuum break lever toward the open choke lever until the lever is against the rear tang on the choke lever.
  18.  
  19. Bend the fast idle cam rod until the bubble on the gauge is centered. Remove the gauge.
  20.  

PRIMARY SIDE VACUUM BREAK ADJUSTMENT
  1. The choke coil lever and the fast idle adjustments must be correct before performing this adjustment.
  2.  
  3. Install a special choke valve measuring gauge (no. J-26701) on the carburetor.
  4.  
  5. Rotate the degree scale until the zero mark is opposite the pointer.
  6.  
  7. With the choke valve completely open, place the magnet directly on top of the choke valve.
  8.  
  9. Rotate the bubble until it is centered.
  10.  
  11. Rotate the scale to place the specified degree opposite the pointer. Refer to the carburetor specification chart.
  12.  
  13. Fully seat the choke vacuum diaphragm using an outside vacuum source.
  14.  
  15. Hold the choke valve toward the closed position by pushing on the intermediate choke lever.
  16.  
  17. Bend the vacuum break rod until the bubble is centered and remove the gauge.
  18.  

Rochester M2MC and M2ME Carburetors-1979-81 Models

All adjustments for this carburetor are the same as for the Rochester M4MC/M4ME, with the exception of the following:

FAST IDLE ADJUSTMENT
  1. Hold the cam follower on the high step of the fast idle cam.
  2.  
  3. Turn the fast idle screw out until the primary throttle valves are closed.
  4.  
  5. Turn the fast idle screw out to contact the lever, then turn the screw in two turns.
  6.  
  7. Check the fast idle speed and adjust by turning the screw.
  8.  

AUTOMATIC CHOKE COIL-M2MC MODELS
  1. Install the thermostatic coil and cover with a gasket between the choke cover and the choke housing. The thermostatic coil must be installed in the slot in the inside of the choke coil lever pick-up arm.
  2.  
  3. Place the fast idle cam follower on the high step of the fast idle cam.
  4.  
  5. Rotate the cover and coil assembly counterclockwise until the choke valve just opens.
  6.  
  7. Align the index point on the cover with the specified mark on the choke housing. The setting is 1 notch lean.
  8.  
  9. Tighten the retaining screws.
  10.  

CHOKE COIL LEVER ADJUSTMENT-M2ME MODELS
  1. Drill out and remove the cover rivets.
  2.  
  3. Remove the cover and coil.
  4.  
  5. Place the fast idle cam follower on the high step of the cam.
  6.  
  7. Push clockwise upward on the thermostatic coil tang until the choke valve is closed.
  8.  
  9. Insert a 0.12 in. (3mm) gauge rod into the hole in the choke housing.
  10.  
  11. The lower edge of the lever should just touch the gauge rod.
  12.  
  13. Bend the choke rod at its mid-point to adjust.
  14.  

Rochester 4MV (Quadrajet) Carburetor-1970-78 Models

FAST IDLE SPEED

See Figure 7



Click image to see an enlarged view

Fig. Fig. 7: View of the fast idle adjustment-Rochester 4MV carburetor

  1. Position the fast idle lever on the high step of the fast idle cam.
  2.  
  3. Be sure that the choke is wide open and the engine warm. On 1973-74 manual transmission models, disconnect the distributor vacuum advance hose.
  4.  
  5. Turn the fast idle screw to gain the proper fast idle rpm.
  6.  

CHOKE ROD (FAST IDLE CAM)
  1. Place the cam follower on the second step of the fast idle cam.
  2.  
  3. Close the choke valve by exerting counterclockwise pressure on the external choke lever.
  4.  
  5. Insert a gauge of the proper size between the lower edge (upper, starting with 1975 models) of the choke valve and the inside air horn wall.
  6.  
  7. To adjust, bend the choke rod.
  8.  

VACUUM BREAK
  1. Fully seat the vacuum break diaphragm using an outside vacuum source.
  2.  
  3. Open the throttle valve enough to allow the fast idle cam follower to clear the fast idle cam. Starting with 1975 models, place the cam follower on the high step.
  4.  
  5. The end of the vacuum break rod should be at the outer end of the slot in the vacuum break diaphragm plunger.
  6.  
  7. The specified clearance should register from the lower end of the choke valve to the inside air horn wall.
  8.  
  9. If the clearance is not correct, bend the vacuum break link.
  10.  

CHOKE UNLOADER
  1. Push up on the vacuum break lever and fully open the throttle valves.
  2.  
  3. Measure the distance from the lower edge (upper, starting with 1975 models) of the choke valve to the air horn wall.
  4.  
  5. To adjust, bend the tang on the fast idle lever.
  6.  

AUTOMATIC CHOKE COIL ROD
  1. Close the choke valve by rotating the choke coil lever counterclockwise.
  2.  
  3. Disconnect the thermostatic coil rod from the upper lever.
  4.  
  5. Push down on the rod until it contacts the bracket of the coil.
  6.  
  7. The rod must fit in the notch of the upper lever.
  8.  
  9. If it does not, it must be bent on the curved portion just below the upper lever.
  10.  

1976 models that hesitate or stall on acceleration during warm-up may be cured by installation of a new choke coil no. 460110.

SECONDARY CLOSING

This adjustment assures proper closing of the secondary throttle plates.

  1. Set the slow idle as per instructions in Engine Electrical . Make sure that the fast idle cam follower is not resting on the fast idle cam.
  2.  
  3. There should be 0.020 in. (0.5mm) clearance between the secondary throttle actuating rod and the front of the slot on the secondary throttle lever with the closing tang on the throttle lever resting against the actuating lever.
  4.  
  5. Bend the tang on the primary throttle actuating rod to adjust.
  6.  

SECONDARY OPENING
  1. Open the primary throttle valves until the actuating link contacts the upper tang on the secondary lever.
  2.  
  3. The bottom of the link should be in the center of the secondary lever slot.
  4.  
  5. Bend the upper tang on the secondary lever to adjust as necessary.
  6.  

FLOAT LEVEL

See Figure 8

Click image to see an enlarged view

Fig. Fig. 8: View of the float adjustment-Rochester 4MV carburetor

  1. Push the float down lightly against the needle, and measure the distance from the air horn gasket surface (gasket removed) to the top of the float at the toe. Measure at a point 3 / 16 in. (4.76mm) back from the toe for all models except for 1973-76, which should be measured at a point 1 / 16 in. (1.58mm) back.
  2.  

Make sure that the retaining pin is firmly hold in place and that the tang of the float is firmly against the needle and seat assembly.

  1. If necessary, remove the float and bend the float arm up or down to adjust to specifications.
  2.  
  3. Check the float alignment after adjusting.
  4.  

ACCELERATOR PUMP
  1. Close the primary throttle valves by backing out the slow idle screw and making sure that the fast idle cam follower is off the steps of the fast idle cam.
  2.  
  3. Bend the secondary throttle closing tang away from the primary throttle lever.
  4.  
  5. With the pump in the inner hole (unless specified otherwise in the carburetor chart) in the pump lever, measure from the top of the choke valve wall to the top of the pump stem.
  6.  
  7. To adjust, bend the pump lever.
  8.  
  9. After adjusting, readjust the secondary throttle tang and the slow idle screw.
  10.  

AIR VALVE SPRING

To adjust the air valve spring windup, loosen the allen head lockscrew and turn the adjusting screw counterclockwise to remove all spring tension. With the air valve closed, turn the adjusting screw clockwise the specified number of turns after the torsion spring contacts the pin on the shaft. Hold the adjusting screw in this position and tighten the lockscrew.

Model M4MC and M4ME Carburetors-1975-86 Models

See Figures 9, 10, 11 and 12



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Fig. Fig. 9: Exploded view of the Rochester M4MC/M4ME carburetor (key list continues on next page)



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Fig. Fig. 10: Rochester M4MC/M4ME carburetor key list (continued)



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Fig. Fig. 11: Exploded view of the Rochester E4ME carburetor



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Fig. Fig. 12: Rochester E4ME carburetor key list

ACCELERATOR PUMP ROD
  1. Take the fast idle cam follower off the fast idle cam steps.
  2.  
  3. Back out the idle speed screw until the throttle valves are completely closed.
  4.  
  5. Be sure that the secondary actuating rod is not preventing the throttle from closing completely. If the primary throttle valves do not close completely, bend the secondary closing tang out of the position, then readjust later.
  6.  
  7. Place the pump rod in the inner hole in the lever, unless specified otherwise in the carburetor chart.
  8.  
  9. Measure the clearance from the top of the choke valve wall, next to the vent stack, and the top of the pump stem.
  10.  
  11. To adjust the dimension, support the pump lever and bend the pump lever.
  12.  
  13. Adjust the idle speed.
  14.  
  15. If necessary, readjust the secondary actuating rod.
  16.  

FAST IDLE SPEED
  1. Hold the cam follower on the high step of the fast idle cam.
  2.  
  3. Turn the fast idle screw out until the primary throttle valves are closed.
  4.  
  5. Turn the fast idle screw in to contact the lever, then turn the screw in 3 turns.
  6.  
  7. Check the fast idle speed, adjust by turning the screw.
  8.  

AUTOMATIC CHOKE COIL LEVER

For M4ME carburetor adjustments, refer to the M2MC/M2ME carburetor adjustment section.

  1. Loosen the three retaining screws and remove the cover and coil assembly from the choke housing.
  2.  
  3. Place the cam follower on the high step of the fast idle cam.
  4.  
  5. Push up on the thermostatic coil tang (counterclockwise) until the choke valve closes.
  6.  
  7. Insert a 0.120 in. (3mm) drill bit into the hole (at about the 4 o'clock position) in the choke housing.
  8.  
  9. The lower edge of the choke coil lever should just contact the side of the bit.
  10.  
  11. Bend the choke rod to adjust.
  12.  

CHOKE ROD (FAST IDLE CAM)

See Figure 13

Click image to see an enlarged view

Fig. Fig. 13: View of the E4ME/MC carburetor fast idle cam adjustment

  1. Adjust the fast idle.
  2.  
  3. Place the cam follower on the second step of the fast idle cam firmly against the ride of the high step.
  4.  
  5. Close the choke valve by pushing up on the choke coil lever inside the choke housing.
  6.  
  7. Measure the clearance between the upper edge of the choke valve and the inside of the air horn wall.
  8.  
  9. Bend the tang on the fast idle cam to adjust the clearance. Be sure that the tang lies against the cam after bending it.
  10.  
  11. Recheck the fast idle speed.
  12.  

AIR VALVE DASHPOT
  1. Seat the front vacuum diaphragm using an outside vacuum source.
  2.  
  3. The air valves must be completely closed.
  4.  
  5. Measure the clearance between the air valve dashpot and the end of the slot in the air valve lever. It should be 0.015 in. (0.38mm).
  6.  
  7. Bend the air valve dashpot to adjust the clearance.
  8.  

FRONT VACUUM BREAK

See Figure 14

Click image to see an enlarged view

Fig. Fig. 14: View of the E4ME/MC carburetor front vacuum adjustment

  1. Remove the thermostatic cover and coil assembly from the choke housing.
  2.  
  3. Place the cam follower on the high step of the fast idle cam.
  4.  
  5. Seat the front vacuum diaphragm using an outside vacuum source.
  6.  
  7. Push up on the inside choke coil lever until the tang on the vacuum break lever contacts the tang on the vacuum break plunger.
  8.  
  9. Measure the clearance between the upper edge of the choke valve and the air horn wall.
  10.  
  11. Turn the adjusting screw on the vacuum break plunger lever to adjust.
  12.  
  13. Reconnect the vacuum hose after adjustment.
  14.  

REAR VACUUM BREAK

See Figure 15

Click image to see an enlarged view

Fig. Fig. 15: View of the E4ME/MC carburetor rear vacuum break adjustment

  1. Remove the thermostatic cover and coil assembly from the choke housing.
  2.  
  3. Place the cam follower on the high step of the fast idle cam.
  4.  
  5. Plug the bleed hose in the vacuum break unit cover with tape.
  6.  
  7. Seat the rear vacuum diaphragm using an outside vacuum source.
  8.  
  9. Push up the choke coil lever inside the choke housing toward the closed position.
  10.  
  11. With the choke rod in the bottom slot of the choke lever, measure the clearance between the upper edge of the choke valve and air horn wall.
  12.  
  13. Bend the vacuum break rod if necessary to adjust.
  14.  
  15. After adjustment, remove the tape and install the vacuum hose.
  16.  

CHOKE UNLOADER
  1. Install the thermostatic coil and cover with a gasket between the choke cover and the choke housing. The thermostatic coil must be installed in the slot in the inside of the choke coil lever pick-up arm.
  2.  
  3. Hold the throttle valves wide open with the choke valve completely closed. On a warm engine, close the choke valve by pushing up on the tang of the intermediate choke lever which contact the fast idle cam. A rubber band will hold it in position.
  4.  
  5. Measure the distance between the upper edge of the choke valve and the air horn wall.
  6.  
  7. Bend the tang on the fast idle lever to adjust the clearance. Check to be sure that the tang on the fast idle cam lever is contacting the center of the fast idle cam after adjustment.
  8.  

AIR VALVE SPRING
  1. Remove the front vacuum break diaphragm and the air valve dashpot rod.
  2.  
  3. Loosen the lockscrew.
  4.  
  5. Turn the tension adjusting screw counterclockwise until the air valve opens part way.
  6.  
  7. Turn the tension adjusting screw clockwise while tapping lightly on the casting with the handle of a screwdriver.
  8.  
  9. When the air valve just closes, turn the tension adjusting screw clockwise the specified number of turns after the spring contacts the pin.
  10.  
  11. Tighten the lockscrew and reinstall the diaphragm and dashpot rod.
  12.  

FLOAT LEVEL

Use the procedure given earlier for the model 4MV, measuring at a point 3 / 16 in. (4.76mm) from the toe of the float.

Rochester E2SE 2-Bbl. Carburetor

See Figures 16 and 17



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Fig. Fig. 16: Exploded view of the Rochester E2SE carburetor (key list appears on next page)



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Fig. Fig. 17: Rochester E2SE carburetor key list

The model E2SE carburetor, introduced on Chevrolet trucks in 1983, is designed as a part of the GM Computer Command Control (C3) system. An electrically operated mixture control solenoid differentiates the E2SE from the conventional 2SE series.

A plunger in the end of the above mentioned solenoid is submerged in fuel in the fuel chamber of the float bowl. The plunger is controlled, or pulsed, by electrical signals received from the Electronic Control Module (ECM). The solenoid system is used to control the air/fuel mixture in the primary bore of the carburetor.

The model E2SE also has a Throttle Position Sensor (TPS) mounted in the float bowl and is used to signal the ECM as throttle position changes occur. As throttle position changes, a tang on the pump lever moves the TPS plunger, modifying an electrical signal to the ECM. This signal is used in conjunction with signals from various other engine sensors by the ECM to control various engine operating modes.

FLOAT ADJUSTMENT

See Figure 18

Click image to see an enlarged view

Fig. Fig. 18: View of the E2SE 2-bbl. carburetor float adjustment

  1. Remove the air horn from the throttle body.
  2.  
  3. Use your fingers to hold the retainer in place, and to push the float down into light contact with the needle.
  4.  
  5. Measure the distance from the tow of the float (furthest from the hinge) to the top of the carburetor (gasket removed).
  6.  
  7. To adjust, remove the float and gently bend the arm to specification. After adjustment, check the float alignment in the chamber.
  8.  

PUMP ADJUSTMENT

See Figure 19

Click image to see an enlarged view

Fig. Fig. 19: View of the E2SE 2-bbl. carburetor pump adjustment

  1. With the throttle closed and the fast idle screw off the steps of the fast idle cam, measure the distance from the air horn casting to the top of the pump stem.
  2.  
  3. To adjust, remove the retaining screw and washer and remove the pump lever. Bend the end of the lever to correct the stem height. Do not twist the lever or bend it sideways.
  4.  
  5. Install the lever, washer and screw and check the adjustment. When correct, open and close the throttle a few times to check the linkage movement and alignment.
  6.  

No pump adjustment is required on 1981 and later models.

FAST IDLE ADJUSTMENT

See Figure 20

Click image to see an enlarged view

Fig. Fig. 20: View of the E2SE 2-bbl. carburetor fast idle adjustment

  1. Set the ignition timing and curb idle speed, and disconnect the plug hoses as directed on the emission control decal.
  2.  
  3. Place the fast idle screw on the highest step of the cam.
  4.  
  5. Start the engine and adjust the engine speed to specification with the fast idle screw.
  6.  

CHOKE COIL LEVER ADJUSTMENT

See Figure 21

Click image to see an enlarged view

Fig. Fig. 21: View of the E2SE 2-bbl. carburetor choke coil lever adjustment

  1. Remove the three retaining screws and remove the choke cover and coil. On models with a riveted choke cover, drill out the three rivets and remove the cover and choke coil.
  2.  

A choke stat cover retainer kit is required for reassembly.

  1. Place the fast idle screw on the high step of the cam.
  2.  
  3. Close the choke by pushing in on the intermediate choke lever. On front wheel drive models, the intermediate choke lever is behind the choke vacuum diaphragm.
  4.  
  5. Insert a drill or gauge of the specified size into the hole in the choke housing. The choke lever in the housing should be up against the side of the gauge.
  6.  
  7. If the lever does not just touch the gauge, bend the intermediate choke rod to adjust.
  8.  

AIR VALVE ROD ADJUSTMENT

See Figure 22

Click image to see an enlarged view

Fig. Fig. 22: View of the E2SE 2-bbl. carburetor air valve rod adjustment

Refer to the accompanying illustration for this procedure.

PRIMARY SIDE VACUUM BREAK ADJUSTMENT

See Figure 23

Click image to see an enlarged view

Fig. Fig. 23: View of the E2SE 2-bbl. carburetor primary vacuum break adjustment

Refer to the accompanying illustration for this procedure.

ELECTRIC CHOKE SETTING

This procedure is only for those carburetors with choke covers retained by screws. Riveted choke covers are preset and nonadjustable.

  1. Loosen the three retaining screws.
  2.  
  3. Place the fast idle screw on the high step of the cam.
  4.  
  5. Rotate the choke cover to align the cover mark with the specified housing mark.
  6.  

CHOKE UNLOADER ADJUSTMENT

See Figure 24

Click image to see an enlarged view

Fig. Fig. 24: View of the E2SE 2-bbl. carburetor choke unloader adjustment

Refer to the accompanying illustration for this procedure.

Rochester E4ME and E4MC Quadrajet 4-Bbl. Carburetor

These 4-bbl. carburetors feature an electrically operated mixture control solenoid, and are designed as part of the GM Computer Command Control (C3) system. As with the E2SE 2-bbl. the electric mixture control solenoid is mounted in the float bowl, and is used to control the air/fuel mixture in the primary bores of the carburetor. The plunger in the solenoid is controlled, or pulsed, by electrical signals received from the Electronic Control Module.

An Idle Speed Control (ISC) assembly, monitored by the ECM, controls engine idle speed. The curb (base) idle is programmed into the ECM and is not adjustable. When the throttle lever is resting against the ISC plunger, the ISC acts as a dashpot on throttle closing. An Idle Speed Solenoid or Idle Load Compensator is used on some models to position the primary throttle valve, providing engine idle speed requirements.

On E4MC models, the Idle Load Compensator (ILC) mounted on the float bowl is used to control curb idle speeds. The ILC uses manifold vacuum to sense changes in engine load (the A/C compressor clutch engaged, for example) and compensates by adjusting throttle angle for the curb idle speed. The ILC uses an spring loaded vacuum sensitive diaphragm whose plunger either extends (vacuum decrease) or retracts (vacuum increase) to adjust throttle angle for curb idle speeds. Both the ISC and ILC are factory adjusted.

FLOAT LEVEL

See Figure 25

Click image to see an enlarged view

Fig. Fig. 25: View of the E4ME/MC carburetor float level adjustment

With the air horn assembly removed, measure the distance from the air horn gasket surface (gasket removed) to the top of the float at the toe 1 / 16 in. (1.58mm) back from the toe).

Make sure the retaining pin is firmly held in place and that the tang of the float is lightly held against the needle and seat assembly.

Remove the float and bend the float arm to adjust except on carburetors used with the computer controlled systems (E4MC and E4ME). For those carburetors, if the float level is too high, hold the retainer firmly in place and push down on the center of the float to adjust. If the float level is too low on models with the computer controlled system, lift out the metering rods. Remove the solenoid connector screw. Turn the lean mixture solenoid screw in clockwise, counting and recording the exact number of turns until the screw is lightly bottomed in the bowl. Then turn the screw out clockwise and remove. Lift out the solenoid and connector. Remove the float and bend the arm up to adjust. Install the parts, turning the mixture solenoid screw in until it is lightly bottomed, then unscrewing it the exact number of turns counted earlier.

ACCELERATOR PUMP

See Figure 26

The accelerator pump is not adjustable on computer controlled carburetors (E4MC and E4ME).

  1. Close the primary throttle valves by backing out the slow idle screw and making sure that the fast idle cam follower is off the steps of the fast idle cam.
  2.  
  3. Bend the secondary throttle closing tang away from the primary throttle lever, if necessary, to insure that the primary throttle valves are fully closed.
  4.  
  5. With the pump in the appropriate hole in the pump lever, measure from the top of the choke valve wall to the top of the pump stem.
  6.  
  7. To adjust, bend the pump lever.
  8.  
  9. After adjusting, readjust the secondary throttle tang and the slow idle screw.
  10.  

REMOVAL & INSTALLATION



See Figures 27, 28, 29, 30 and 31


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

  1. Remove the air cleaner and its gasket.
  2.  
  3. Disconnect the fuel and vacuum lines from the carburetor.
  4.  
  5. Disconnect the choke coil rod or heated air line tube.
  6.  
  7. Disconnect the throttle linkage.
  8.  
  9. On automatic transmission cars, disconnect the throttle valve linkage.
  10.  
  11. Remove the CEC valve vacuum hose and electrical connector.
  12.  



Click image to see an enlarged view

Fig. Fig. 26: View of the E4ME/MC carburetor accelerator pump adjustment



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Fig. Fig. 27: Tag and disengage all the vacuum lines



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Fig. Fig. 28: Tag and disengage any electrical connections that will impede the carburetor removal



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Fig. Fig. 29: When disconnecting the fuel lines, make sure to use a backup line wrench



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Fig. Fig. 30: Unfasten the carburetor retaining bolts



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Fig. Fig. 31: After all the linkages have been tagged and disengaged, remove the carburetor from the vehicle

  1. Remove the idle stop electrical wiring from the idle stop solenoid, if so equipped.
  2.  
  3. Remove the carburetor attaching nuts and/or bolts, gasket or insulator, and remove the carburetor.
  4.  
  5. Install the carburetor using a reverse of the removal procedure. Use a new gasket and fill the float bowl with gasoline to ease starting the engine.
  6.  

IDENTIFICATION



Carburetor identification numbers will generally be found in the following locations:



1 MV, ME: Stamped on the vertical portion of the float bowl, adjacent to the fuel inlet nut.
 
2 GV, GC: Stamped on the flat section of the float bowl next to the fuel inlet nut.
 
E2SE, 2SE: Stamped on the vertical surface of the float bowl adjacent to the vacuum tube.
 
M2MC: Stamped on the vertical surface of the left rear corner of the float bowl.
 
E4ME, 4 MV, M4MC, M4ME: Stamped on the vertical section of the float bowl, near the secondary throttle lever.
 

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 you carburetor in a clean, dust free area. Carefully disassembly the carburetor, referring often to the exploded views and directions packaged with the rebuilding kit. 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 parts in the solvent any longer than is necessary to sufficiently loosen the deposits. Excessive cleaning may remove the special finish from the float bowl and choke valve bodies, leaving these parts unfit for service. Soak all parts in clean solvent and blow them dry with compressed air or allow them to air dry. Wipe clean all cork, plastic, leather, and fiber parts with a 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.

Check all parts for wear or damage. If wear or damage is found, replace the defective parts.

Especially check 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 shafts and bushings are not included in overhaul kits. They can be purchased separately.

  1. Inspect the idle mixture adjusting needles for burrs or 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 breath 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 parts supplied with the kit (especially gaskets) can result in poor performance later.

Some carburetor manufacturers supply overhaul kits of three basic types: minor repair; major repair; and gasket kits.

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 tight in their seats, buy do not overtighten as the tips 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 when reassembling.

 
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