GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Carburetor Adjustments

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ADJUSTMENTS



Float Level

See Figures 1, 2 and 3

MODELS 2GC, GE, GV
  1. Remove the air horn assembly from the carburetor.
  2.  
  3. Hold the air horn assembly upside down and measure the distance from the air horn gasket to the lip at the toe of the float. See the chart for the proper measurement.
  4.  
  5. Bend the float arm to adjust the float level to the proper specifications.
  6.  



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Fig. Fig. 1: Model 2GC, GV, GE float adjustment

ALL OTHER 2 & 4 BBL MODELS, EXCEPT 1985-90
  1. Remove the air horn.
  2.  
  3. Hold the float retainer in place and lightly push down on the float against the needle.
  4.  
  5. Measure the gap between the casting surface and the top of the float at a point 3 / 16 in. (4.7mm) back from the float toe.
  6.  
  7. To adjust, remove the float and bend the float arm.
  8.  
  9. On CCC and C-4 carburetors, if the float level varies more than 1 / 16 in. (1.6mm) either way, adjust as follows:
    1. Level too high. Hold the float retainer firmly in place and push down on the center of the float body until the correct gap is attained.
    2.  
    3. Level too low: Lift out the metering rods. Remove the solenoid connector screw. Turn the lean mixture solenoid screw clockwise counting the number of turns until the screw is lightly seated. Then, remove the screw. Lift the solenoid and connector from the float bowl. Remove the float and bend the arm to adjust. Install the float and check the adjustment. Install the mixture screw to the exact number of turns noted earlier. Install all other parts.
    4.  

  10.  



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Fig. Fig. 2: Float adjustment; 2 and 4 BBL models through 1984

1985-90 2 & 4 BBL MODELS

To make this adjustment, you will need a number of special tools. They are: GM Part No. J-34817-1, J-34817-3, J-9789-90, and J-34817-15 or equivalent.

  1. The solenoid plunger, metering rods, and float bowl insert must be removed. Then attach J-34817-1 to the float bowl and place J-34817-3 into it with the contact pin resting on the outer edge of the float lever.
  2.  
  3. Use J-9789-90 to measure the distance from the top of the casting to the top of the float at a point 3 / 16 in. (4.7mm) from the large end of the float.
  4.  
  5. If the reading is more than 1 / 16 in. (1.6mm) either above or below the specification, use J-34817-15 to bend the lever up or down. Specifications are:

    1985 E2ME carburetor numbers 17085192 and 17085194 - 11 / 32 in. (8.7mm)
     
    All other 1985 E2ME and 1986-87 E2ME - 5 / 16 in. (7.9mm)
     
    1985-90 E4MC - 11 / 32 in. (8.7mm).
     

  6.  

Remove this tool and remeasure. Repeat the procedure until the specification is met within the tolerance above or in the carburetor specification chart.



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Fig. Fig. 3: Float adjustment; 2 and 4 BBL models 1985-1990

Vacuum Breaks

See Figures 4, 5, 6, 7, 8, 9 and 10

MODELS 2GV, GE, GC
  1. Remove the air cleaner. Vehicles equipped with TAC air cleaners should have the sensor's vacuum take-off port plugged.
  2.  
  3. Using an external vacuum source, apply vacuum to the vacuum break diaphragm until the plunger is fully seated. Or, fully seat the plunger and place a piece of tape over the hose fitting.
  4.  
  5. When the plunger is seated, push the choke plate toward the closed position. Place the idle speed screw on the high step of the fast idle cam.
  6.  
  7. Holding the choke plate in the closed position, place the specified size gauge between the upper edge of the choke plate and the air horn wall.
  8.  
  9. If the measurement is not correct, bend the vacuum break rod.
  10.  



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Fig. Fig. 4: Vacuum break adjustment; 2GC, GE, GV models

ALL OTHER 2 BBL MODELS TO 1980
  1. Place the cam follower on the highest step of the fast idle cam.
  2.  
  3. Seat the vacuum break diaphragm by using an outside vacuum source.
  4.  
  5. Remove the choke cover and coil, then push up on the coil lever until the tang on the vacuum break lever contacts the tang on the vacuum break plunger stem. Compress the backing spring for rich adjustment only.
  6.  
  7. With the choke rod in the bottom of the choke lever slot, measure the distance between the upper edge of the choke plate and the inside wall of the air horn.
  8.  
  9. Bend the link rod at the vacuum break plunger stem to adjust the lean setting. Bend the link rod at the opposite from the diaphragm to adjust the rich setting.
  10.  



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Fig. Fig. 5: Rich setting; 2 BBL models through 1980



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Fig. Fig. 6: Lean setting; 2 BBL models through 1980

4 BBL MODELS TO 1980
  1. Place the cam follower lever on the highest step of the fast idle cam.
  2.  
  3. Remove the choke cover and coil assembly from the choke housing.
  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. Place the proper size gauge between the upper edge of the choke plate and the inside of the air horn wall.
  10.  
  11. To adjust, turn the adjustment screw on the vacuum break plunger lever.
  12.  
  13. To adjust the secondary vacuum break, with the choke cover and coil removed, the cam follower on the highest step of the fast idle cam, tape over the bleed hole in the rear vacuum break diaphragm.
  14.  
  15. Seat the rear diaphragm using an outside vacuum source.
  16.  
  17. Close the choke by pushing up on the choke coil lever inside the choke housing. Make sure the choke rod is in the bottom of the slot in the choke lever.
  18.  
  19. Measure between the upper edge of the choke plate and the air horn wall with a wire type gauge.
  20.  
  21. To adjust, bend the vacuum break rod at the first bend near the diaphragm.
  22.  



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Fig. Fig. 7: Front vacuum break adjustment; 4 BBL models through 1980



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Fig. Fig. 8: Rear vacuum break adjustment; 4 BBL models through 1980

2 & 4 BBL MODELS 1981 AND LATER
  1. To adjust the front vacuum break, attach a rubber band to the vacuum break lever of the intermediate choke shaft.
  2.  
  3. Open the throttle to allow the choke valve to close.
  4.  
  5. Set an angle gauge such as J-26701-A, BT-7704 or equivalent and set to specifications.
  6.  
  7. Plug the vacuum break plunger. Apply 15 in. Hg (51 k Pa) of vacuum to seat the vacuum break plunger. On some models, seat the bucking spring.
  8.  
  9. Adjust if the bubble is not recentered, by turning the screw.
  10.  
  11. To adjust the rear vacuum break, attach a rubber band to the vacuum break lever of the intermediate choke shaft.
  12.  
  13. Open the throttle to allow the choke valve to close.
  14.  
  15. Set up the angle gauge J-26701-A, BT-7704 (or equivalent) and set to specifications.
  16.  
  17. Plug the vacuum break plunger. Apply 15 in. Hg (51 k Pa) of vacuum to seat the vacuum break plunger. Compress the plunger bucking spring, if so equipped.
  18.  
  19. Adjust if the bubble is not recentered, by either:
    1. Supporting the "S" and bending the vacuum break link.
    2.  
    3. Or, turning the screw with a 1 / 8 in. hex wrench.
    4.  

  20.  



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Fig. Fig. 9: Front vacuum break adjustment; 2 and 4 BBL models 1981-1990



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Fig. Fig. 10: Rear vacuum break adjustment; 2 and 4 BBL models 1981-1990

Choke Unloader
MODELS 2GC, GE, GV

See Figures 11, 12 and 13

  1. Hold the throttle valves wide open.
  2.  
  3. Hold the choke valve towards the closed position with a rubber band.
  4.  
  5. Bend the unloader tang on the throttle lever to obtain the specified clearance between the upper edge of the choke plate and the air horn wall.
  6.  



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Fig. Fig. 11: Unloader adjustment; 2GC, GE, GV models

ALL OTHER 2 BBL MODELS AND 4 BBL MODELS TO 1980
  1. With the choke plate completely closed, hold the throttle plates wide open.
  2.  
  3. Measure the distance between the upper edge of the choke plate and the airhorn wall.
  4.  
  5. Bend the tang on the fast idle lever to adjust.
  6.  



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Fig. Fig. 12: Unloader adjustment; 2 and 4 BBL models through 1980

2 & 4 BBL MODELS 1981 AND LATER
  1. Attach a rubber band to the vacuum break intermediate choke shaft.
  2.  
  3. Open the throttle to allow the choke valve to close.
  4.  
  5. Set an angle gauge such as J-26701-A, BT-7704 or equivalent, to the angle specification in the specification chart in this information.
  6.  
  7. Hold the secondary throttle lockout lever away from the pin.
  8.  
  9. Hold the throttle lever in the wide open position.
  10.  
  11. Adjust, if the bubble is not recentered, by bending the fast idle lever using a bending tool such as J-9789 or B-3006M.
  12.  



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Fig. Fig. 13: Unloader adjustment; 2 and 4 BBL models 1981 and later

Fast Idle Cam
MODELS 2GC, GE, GV

See Figures 14, 15 and 16

  1. Place the idle speed screw on the second step of the fast idle cam against the shoulder of the high step for 2GV models, and on the highest step for the GC and GE models.
  2.  
  3. Push the choke plate closed.
  4.  
  5. On 2GV models, measure the distance between the upper edge of the choke plate and the air horn wall. To adjust, bend tang. On GE and GC models, insert the specified gauge into the choke housing slot. Choke coil lever should just contact gauge in the end of the slot. Adjust by bending "U" bend of the rod.
  6.  



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Fig. Fig. 14: Fast idle cam adjustment; 2GE, GC, GV

ALL OTHER 2 BBL MODELS AND 4 BBL MODELS TO 1980
  1. Place the cam follower on the second step of the fast idle cam.
  2.  
  3. Close the choke plate by pushing counterclockwise on the external choke lever. On 1975-80 models, remove the coil assembly from the choke housing and push on the choke coil lever.
  4.  
  5. Measure between the upper edge of the choke plate and the air horn wall.
  6.  
  7. To adjust, bend the tang on the fast idle cam. Be sure that the tang rests against the cam after bending.
  8.  



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Fig. Fig. 15: Fast idle cam adjustment; 2 and 4 BBL models through 1980

2 & 4 BBL MODELS 1981 AND LATER
  1. Attach a rubber band to the vacuum break lever of the intermediate choke shaft.
  2.  
  3. Open the throttle to allow the choke valve to close.
  4.  
  5. Set up an angle gauge such as J-26701-A or BT-7704 and set to specifications.
  6.  
  7. Place the fast idle cam on the second step with the lever contacting the rise of the high step.
  8.  
  9. Adjust if the bubble is not centered, by bending the tang on the fast idle cam.
  10.  



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Fig. Fig. 16: Fast idle cam adjustment; 2 and 4 BBL models 1981-1990

Air Valve Link (Dashpot)

See Figure 17

ALL 4 BBL MODELS
  1. Seat the front vacuum break diaphragm by using an outside vacuum source.
  2.  
  3. The air valves must be closed completely.
  4.  
  5. Measure the clearance between the air valve dashpot and the end of the slot in the air valve lever. The clearance should be 0.050 in. (1.27mm) on models through 1981. Later models use a clearance of 0.025 in. (0.635mm).
  6.  
  7. Bend the air valve link (dashpot) rod, if necessary, to adjust.
  8.  



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Fig. Fig. 17: Air valve link adjustment; all 4 BBL models

Choke Coil Lever
MODELS 2GV, GC, GE

See Figures 18 and 19

  1. Remove the choke coil lever.
  2.  
  3. Place the idle speed screw on the highest step of the fast idle cam.
  4.  
  5. Close the choke valve.
  6.  
  7. The edge of the coil lever must line up with the edge of a 0.120 in. plug gauge in the hole inside the choke housing.
  8.  
  9. Bend lever rod to adjust.
  10.  



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Fig. Fig. 18: Choke coil lever adjustment; 2GE, GC, GV models

ALL EXCEPT 2GV, GC, GE MODELS
  1. Remove the choke cover and thermostatic coil from the choke housing.
  2.  
  3. Push the coil tang counterclockwise until the choke plate is fully closed.
  4.  
  5. Insert a 0.120 in. (3mm) gauge into the hole in the choke housing. The lower edge of the choke coil lever should just contact the side of the gauge.
  6.  
  7. Bend the choke rod to adjust, if necessary.
  8.  



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Fig. Fig. 19: Choke coil lever adjustment; all except 2GV, GC, GE models

Automatic Choke Coil
ALL EXCEPT 2GC, GE, GV MODELS
  1. Place the idle speed screw or follower on the highest step of the fast idle cam.
  2.  
  3. Loosen the choke coil cover retaining screws.
  4.  

The choke coil may be riveted onto the carburetor housing on most later model vehicles. Drill and remove the rivet head by using a5/16in. (0.159) drill bit. Punch the remainder of the rivet out of the choke housing. Use the same size rivet for installation.

  1. Rotate the choke cover counterclockwise until the choke plate just closes.
  2.  
  3. Align the index mark on the choke cover with the specified point on the choke housing. Tighten the cover screws or install new rivets.
  4.  

Accelerator Pump Rod

See Figures 20 and 21

MODELS 2GC, GE, GV
  1. Back out throttle stop screw and fast idle screw so that throttle valves are completely closed.
  2.  
  3. Measure distance from the top of the air horn ring to the top of the pump connector rod at the pump lever.
  4.  
  5. If distance is incorrect, adjust by bending pump connector rod at the existing bend.
  6.  



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Fig. Fig. 20: Pump rod adjustment; 2GC, GV, GE models

ALL OTHER MODELS

This adjustment is not required on C-4 and CCC carburetors.

  1. With the throttle valves completely closed, make sure fast idle cam follower is off the steps on the fast idle cam.
  2.  
  3. Make sure the pump rod is in the specified hole.
  4.  
  5. Gauge from top of choke valve wall, next to the vent stack, to the top of the pump stem.
  6.  
  7. Bend pump lever to adjust.
  8.  



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Fig. Fig. 21: Pump rod adjustment; all other models

Air Valve Spring

See Figure 22

ALL 4 BBL MODELS
  1. Loosen lock screw using special hex wrench.
  2.  
  3. Turn tension adjusting screw counterclockwise until air valve opens part way.
  4.  
  5. Turn tension adjusting screw clockwise until air valve just closes, then turn the screw clockwise the specified number of turns.
  6.  
  7. Tighten lock screw.
  8.  



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Fig. Fig. 22: Air valve spring adjustment, all 4 BBL models

 
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