Repair Pontiac Mid-size 1974-1983 Repair Guide

Carburetor

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REMOVAL & INSTALLATION





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Fig. Fig. 1 Carburetor identification number location



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Fig. Fig. 2 Components of a typical Rochester 4-bbl. carburetor



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Fig. Fig. 3 1. Fuel line



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Fig. Fig. 4 To remove the carburetor, tag and disconnect all necessary fuel and vacuum lines



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Fig. Fig. 5 Detach the carburetor electrical connections



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Fig. Fig. 6 Remove the small clip retaining the throttle cable ...



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Fig. Fig. 7 ... then detach the throttle cable from the carburetor



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Fig. Fig. 8 Use needlenose pliers to remove the clip ...



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Fig. Fig. 9 ... then remove the linkage from the clamp



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Fig. Fig. 10 If necessary, detach any remaining electrical connectors



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Fig. Fig. 11 Remove the carburetor mounting bolts



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Fig. Fig. 12 An extension may be helpful to access some of the carburetor mounting bolts



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Fig. Fig. 13 Remove the carburetor from the intake manifold ...



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Fig. Fig. 14 ... then remove and discard the carburetor gasket. Always use a new gasket during assembly

  1. Remove the air cleaner assembly.
  2.  
  3. Tag and disconnect all vacuum lines, electric wires and fuel lines from the carburetor. Tag and disconnect the throttle linkage.
  4.  
  5. Disconnect the automatic transmission downshift linkage.
  6.  
  7. Disconnect the idle solenoid wiring.
  8.  
  9. Remove the carburetor attaching nuts and remove the carburetor.
  10.  
  11. Installation is in the reverse order of removal. Use a new gasket and fill the float bowl with fuel to ease starting.
  12.  

ADJUSTMENTS



Float Level
MV CARBURETOR


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Fig. Fig. 15 Float level adjustment-MV 1-barrel carburetor

  1. Remove the top of the carburetor if you have not done so already.
  2.  
  3. Hold the float retainer in place and the float arm against the top of the float needle by pushing down on the top of the float arm at the outer end toward the float bowl casting.
  4.  
  5. Using an adjustable T-scale, measure the distance from the top of the float to the float bowl gasket surface. See the specifications chart for the proper measurement.
  6.  

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

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

5210-C AND 6510-C CARBURETORS


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Fig. Fig. 16 Float level adjustment-5210-C carburetor

  1. With the carburetor air horn inverted, and the float tang resting lightly on the inlet needle, insert the specified gauge between the air horn and the float.
  2.  
  3. Bend the float tang if an adjustment is needed.
  4.  

2GC, 2GE AND 2GV CARBURETORS


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Fig. Fig. 17 Float level adjustment-2GC, GE and GV carburetors

  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.  

2MC CARBURETOR
  1. Remove the air horn assembly from the carburetor. Remove the gasket.
  2.  
  3. Measure the distance from the air horn gasket surface to the top of the float at the toe ( 1 / 16 in. back from the toe on 1974 and 1975 models; 3 / 16 in. back on 1976 and later models).
  4.  
  5. After making sure the retaining pin is in place, bend the float arm to adjust the float level.
  6.  

E2MC, E2ME, E4MC AND E4ME CARBURETORS


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Fig. Fig. 18 Float level adjustment-2MC carburetor shown, M2ME and E2ME similar

  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 inch back from the float toe.
  6.  
  7. To adjust, remove the float and bend the float arm.
  8.  
  9. On CCC carburetors, if the float level varies more than 1 / 16 either way, adjust as follows:
  10.  
    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.  


M4MC CARBURETOR


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Fig. Fig. 19 Float level adjustment-M4MC carburetor

  1. With the air horn assembly and gasket removed from the carburetor, measure the distance from the air horn gasket surface to the top of the float at the toe.
  2.  
  3. To adjust the float level, bend the float arm by pushing on the pontoon.
  4.  
  5. After the adjustment, check the float alignment.
  6.  

Choke Coil Lever
MV CARBURETOR
  1. Place the fast idle speed screw on the highest step of the fast idle cam.
  2.  
  3. Hold the choke plate fully closed.
  4.  
  5. Insert a 0.120 in. gauge through the hole in the arm on the choke housing and into the hole in the casting.
  6.  
  7. Bend the link to adjust.
  8.  

2 AND 4-BBL. CARBURETORS


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Fig. Fig. 20 Choke coil lever adjustment-2GC and 2GE carburetors



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Fig. Fig. 21 Choke coil lever adjustment-2MC and 4MC carburetors

  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. 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.  

Automatic Choke
MV CARBURETOR
  1. Place the fast idle cam follower on the high step of the cam.
  2.  
  3. Loosen the three retaining screws and rotate the cover counterclockwise until the choke plate just closes.
  4.  
  5. Align the index mark on the cover with the specified housing mark. Tighten the three screws.
  6.  

2-BBL. CARBURETORS
  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.  
  5. Rotate the choke cover counterclockwise until the choke plate just closes.
  6.  
  7. Align the index mark on the choke cover with the specified point on the choke housing.
  8.  

4-bbl. Carburetors
  1. Loosen the choke housing cover screws.
  2.  
  3. Place the fast idle cam follower on the highest step of the fast idle cam.
  4.  
  5. Rotate the cover and coil assembly counterclockwise until the choke plate just closes.
  6.  
  7. Align the index mark on the cover with the specified index point on the housing.
  8.  
  9. Tighten the retaining screws.
  10.  

Choke Unloader
MV CARBURETOR


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Fig. Fig. 22 Choke unloader adjustment-MV 1-bbl. carburetor

  1. Hold the throttle valve wide open.
  2.  
  3. Hold-down the choke plate with your finger and insert the specified gauge between the upper edge of the choke plate and the airhorn wall.
  4.  
  5. Bend the linkage tang to adjust.
  6.  

5210-C AND 6510-C CARBURETORS


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Fig. Fig. 23 Choke unloader adjustment-5210-C and 6510-C 2-bbl. carburetors

  1. Place the throttle in the wide open position.
  2.  
  3. Insert a 0.350 or 0.400 in. gauge (see chart) between the lower edge of the choke valve and the air horn wall.
  4.  
  5. Bend the tang of the choke arm to adjust.
  6.  

1974-80 2GE, 2GC AND 2MC CARBURETORS


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Fig. Fig. 24 Choke unloader adjustment-2GE and 2GC carburetors



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Fig. Fig. 25 Choke unloader adjustment-2MC carburetor

  1. Hold the throttle plates wide open.
  2.  
  3. Close the choke plate.
  4.  
  5. Bend the unloader tang to obtain the proper clearance between the upper edge of the choke plate and the airhorn wall.
  6.  

1974-80 4-BBL. CARBURETORS


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Fig. Fig. 26 Choke unloader adjustment-M4MC 4-bbl. carburetor

  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.  

1981-83 2 AND 4-BBL. CARBURETORS

The unloader adjustment on these carburetors requires special tools and is quite complicated. Service here is best left to a professional mechanic.

Vacuum Break
MV CARBURETOR


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Fig. Fig. 27 Vacuum break adjustment-1974-75 MV 1-barrel carburetor

  1. On vehicles equipped with TAC air cleaners, plug the sensor's vacuum take-off port after removing the air cleaner.
  2.  
  3. Using an external vacuum source, apply vacuum to the vacuum break diaphragm until the plunger is fully seated.
  4.  
  5. After the plunger is seated, push the choke plate fully closed.
  6.  

5210-C CARBURETOR
  1. Remove the three hex-headed screws and ring which retain the choke cover.
  2.  
  3. Push the diaphragm shaft against the stop. Push the coil lever clockwise.
  4.  
  5. Insert the specified size gauge on the down side of the primary choke plate.
  6.  
  7. Take the slack out of the linkage and turn the adjusting screw with a 5 / 22 in. Allen wrench.
  8.  

6510-C CARBURETOR


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Fig. Fig. 28 Vacuum break adjustment-5210-C and 6510-C carburetors

  1. Remove the choke coil assembly.
  2.  
  3. Push the choke coil lever clockwise to close the choke valve.
  4.  
  5. Push the choke shaft against its stop.
  6.  
  7. Take the slack out of the linkage, in the open direction.
  8.  
  9. Insert the specified gauge between the lower edge of the choke plate and the air horn wall. Turn the adjusting screw in the diaphragm housing to adjust.
  10.  

2GC AND 2GE CARBURETORS


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Fig. Fig. 29 Vacuum break adjustment-2GC and 2GE carburetors

  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.
  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.  

2MC CARBURETOR


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Fig. Fig. 30 Rich vacuum break setting-2MC carburetor



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Fig. Fig. 31 Lean vacuum break setting-2MC carburetor

  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 and 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 slot in the choke lever, 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.  

1975-80 4-BBL. CARBURETORS


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Fig. Fig. 32 Front vacuum break adjustment-typical 4-bbl. carburetor



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Fig. Fig. 33 Rear vacuum break adjustment-4-bbl. carburetors without adjusting screw, through 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 diphragm.
  22.  

1981-83 2 AND 4-BBL. CARBURETORS

These carburetors require special tools for adjustment. Service is best left to a professional mechanic.

Fast Idle Cam
MV CARBURETOR


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Fig. Fig. 34 Fast idle cam adjustment-1MV 1-bbl. carburetor through 1975

  1. Adjust curb idle speed with solenoid (if equipped). Hold the fast idle speed screw on the second cam step against the shoulder of the high step.
  2.  
  3. Hold the choke plate closed.
  4.  
  5. Measure the distance between the center upper edge of the choke plate and the air horn wall.
  6.  
  7. Bend the linkage rod at the upper angle to adjust the clearance.
  8.  

5210-C AND 6510-C CARBURETORS


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Fig. Fig. 35 Fast idle cam adjustment-5210-C and 6510-C carburetors

  1. Set the fast idle cam so that the screw is held against the second high step of the fast idle cam.
  2.  
  3. Insert the specified drill bit or gauge on the "down" side of the choke plate (between the lower edge of the choke valve and inside the choke wall).
  4.  
  5. If adjustment is necessary, bend the tang (see illustration).
  6.  

2GC AND 2GE CARBURETORS
  1. Turn the idle speed screw in until it just contacts the lower step of the fast idle cam. Then, turn the screw in one full turn.
  2.  
  3. Place the idle speed screw on the second step of the fast idle cam against the shoulder of the high step.
  4.  
  5. Measure the distance between the upper edge of the choke plate and the air horn wall. Push the choke plate closed first.
  6.  
  7. If adjustment is required, bend the choke lever tang.
  8.  

2MC CARBURETORS
  1. Adjust the fast idle speed.
  2.  
  3. Place the cam follower lever on the second step of the fast idle cam, holding it firmly against the shoulder of the high step.
  4.  
  5. Close the choke coil lever inside the choke housing.
  6.  
  7. Gauge between the upper edge of the choke plate and the inside of the air horn wall.
  8.  
  9. Bend the tang on the intermediate choke lever to adjust.
  10.  

4-BBL. CARBURETORS


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Fig. Fig. 36 Fast idle cam adjustment-2MC and 4MC carburetors

  1. Adjust the fast idle and 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 chock 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, 1975-80 models, bend the tang on the fast idle cam. Be sure that the tang rests against the cam after bending.
  8.  

Air Valve Dashpot
4-BBL. CARBURETORS
  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.
  6.  
  7. Bend the air valve dashpot rod, if necessary, to adjust.
  8.  

OVERHAUL





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Fig. Fig. 37 Air horn tightening sequence-2GC, GE and GV carburetors



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Fig. Fig. 38 Air horn tightening sequence-M2MC carburetor



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Fig. Fig. 39 Air horn tightening sequence-M4MC carburetor

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 your carburetor in a clean, dusted free area. Carefully disassemble 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. Rinse 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. Basically, they contain the following,

Minor Repair Kits:



All gaskets
 
Float needle valve
 
All diaphragms
 
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 tight in their seats, but do not overtighten as the tips will be distorted. Tighten all screws gradually, in rotation. DO NOT tighten needle valves into their seats; needle valve and valve seat damage will occur, along with uneven jetting. Always use new gaskets. Be sure to adjust the float level when reassembling.



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Fig. Fig. 40



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Fig. Fig. 41



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Fig. Fig. 42



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Fig. Fig. 43



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Fig. Fig. 44



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Fig. Fig. 45



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Fig. Fig. 46



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Fig. Fig. 47



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Fig. Fig. 48



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Fig. Fig. 49

 
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