Chevrolet Blazer/Jimmy 1969-1982 Repair Guide

Carburetor

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Fig. Fig. 1 Carburetor Application

REMOVAL & INSTALLATION





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Fig. Fig. 2 When removing the carburetor, first tag and disconnect the fuel lines



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Fig. Fig. 3 Use a flare nut wrench and a back-up wrench to loosen the fuel line retaining nut ...



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Fig. Fig. 4 ... then gently separate the line from the carburetor



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Fig. Fig. 5 1. Throttle cable 2. Retaining clip 3. Return spring Remove the throttle cable retaining clip ...



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Fig. Fig. 6 ... then disconnect the throttle cable



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Fig. Fig. 7 Disengage the throttle lever return spring



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Fig. Fig. 8 Loosen the carburetor retaining bolts ...



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Fig. Fig. 9 ... then remove the bolts from the carburetor



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Fig. Fig. 10 Remove the carburetor from the engine ...



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Fig. Fig. 11 ... then remove the carburetor base gasket

  1. Remove the air cleaner and mounting 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 models, disconnect the throttle valve linkage.
  10.  
  11. Remove all vacuum hoses and electrical connectors.
  12.  
  13. Remove the idle stop electrical wiring from the idle stop solenoid, if so equipped.
  14.  
  15. Remove the carburetor attaching nuts and/or bolts, gasket or insulator, and remove the carburetor.
  16.  
  17. Install the carburetor using a reverse of the removal procedure. Use a new gasket and tighten the mounting bolts evenly.
  18.  

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 your carburetor in a clean, dust-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 busings 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, but 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.

ADJUSTMENTS



These adjustments are arranged by carburetor model. All Blazers and Jimmys 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.

The following should be tended to before attempting any running adjustments.

  1. Thoroughly warm up the engine. Be sure that it is at normal operating temperature.
  2.  
  3. Check all carburetor mounting nuts. Also check the intake manifold-to-cylinder head bolts. If air is leaking at these points, attempts at adjustment will lead to frustration.
  4.  
  5. Check the manifold heat control valve (if used) to be sure that it is free.
  6.  
  7. Make sure that the choke is fully open.
  8.  
  9. Make sure that the idle speed and mixture ( ) are correct. The engine should be idling smoothly.
  10.  

Model MV (1969-74 Vehicles)


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Fig. Fig. 12 Exploded view of the Rochester MV carburetor

FAST IDLE SPEED


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Fig. Fig. 13 Fast idle adjustment-MV carburetors

The fast idle speed adjustment must be made with the manual transmission in Neutral and the automatic in Park.

  1. Position the fast idle lever on the high step or position 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. Disconnect the distributor vacuum advance hose on 1974 manual transmission models.
  4.  
  5. Bend the fast idle lever, using the screwdriver slot, until the specified speed is obtained.
  6.  

CHOKE ROD (FAST IDLE CAM)


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Fig. Fig. 14 Fast idle cam (choke rod) adjustment-MV carburetors

Adjust the fast idle speed 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. If the cam has no steps, align the cam index line with the tang contact point.
  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


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Fig. Fig. 15 Vacuum break adjustment-MV carburetors

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 fully seated.
  4.  
  5. When the plunger is seated, push the choke valve toward the closed position. The vacuum break rod should be in the end of the slot.
  6.  
  7. Holding the choke valve in this position, place the specified gauge between the lower edge of the choke valve and the air horn wall.
  8.  
  9. If the measurement is not correct, bend the vacuum break rod at the angle.
  10.  

CHOKE UNLOADER


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Fig. Fig. 16 Choke unloader adjustment-MV carburetors

  1. Apply pressure to the choke valve and hold it in the closed position. The rod should be in the end of the slot.
  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


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Fig. Fig. 17 Automatic choke coil rod adjustment-MV carburetors

  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 of the hole in the choke lever.
  6.  
  7. To make adjustments, bend the rod at the center.
  8.  

FLOAT LEVEL


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Fig. Fig. 18 Float level adjustment-MV carburetors

  1. Remove the top of the carburetor. Hold the float retainer pin in place and the float arm against the top of the float needle by pushing down on the float arm at the outer end toward the float bowl casting.
  2.  
  3. Using an adjustable T scale, measure the distance from the toe 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


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Fig. Fig. 19 Metering rod-MV carburetors

  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 or idle stop solenoid 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 gauge between the bowl casting sealing bead 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 inner end. After adjustment, reinstall the metering rod.
  12.  

IDLE VENT (1969 MODELS)
  1. The engine idle must be set at the specified rpm and the choke valve held wideopen so that the fast idle cam follower is not contacting the cam.
  2.  

If the carburetor is off the engine, a preliminary idle setting can be made by turning the idle speed screw in 1 1 / 2 turns 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. To check, a drill bit 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.

COMPUTERIZED ENGINE 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 (1975-78 Vehicles)

Any adjustments not illustrated for the 1MV or 1ME are similar to those for the MV. Be sure to check the text against the illustration, since some gauge points will change.

FAST IDLE SPEED


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Fig. Fig. 20 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)


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Fig. Fig. 21 Fast idle cam (choke rod) adjustment-1MV and 1ME carburetors

  1. Check and adjust the fast idle speed.
  2.  
  3. Set the fast idle exam 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 and 1978) 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


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Fig. Fig. 22 Choke unloader adjustment-1MV carburetors



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Fig. Fig. 23 Choke unloader adjustment-1ME carburetors

  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 (lower for 1978) 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

This adjustment is the same as for the Model MV, shown earlier.

AUTOMATIC CHOKE COIL ROD (1975 MODELS)


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Fig. Fig. 24 Automatic choke coil rod adjustment-1975 1MV carburetors

  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.  

AUTOMATIC CHOKE (1977-78 1ME MODELS)


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Fig. Fig. 25 Electric choke adjustments-1ME carburetors

  1. Loosen the three choke housing retaining screws.
  2.  
  3. Place the cam follower on the high step of the cam.
  4.  
  5. Set the mark on the electric choke to the center mark on the index.
  6.  
  7. Tighten the housing screws.
  8.  

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.  

AUXILIARY VACUUM BREAK (1975 MODELS)


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Fig. Fig. 26 Auxiliary vacuum break adjustment-1975 1MV carburetors

  1. With an 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.  

VACUUM BREAK (1976-77 MODELS)


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Fig. Fig. 27 Vacuum break adjustment-1976-77 1MV and 1ME carburetors

  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.  

VACUUM BREAK (1978 MODELS)


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Fig. Fig. 28 Vacuum break adjustment-1978 1ME carburetors

  1. Place the cam follower on the high step of the cam.
  2.  
  3. Apply vacuum in order to seat the diaphragm.
  4.  
  5. Push down on the choke valve. Compress the plunger spring and seat the plunger stem, if so equipped.
  6.  
  7. Measure the distance between the lower edge of the choke valve and the inside air horn wall.
  8.  
  9. Bend the link to adjust to specification.
  10.  

Model 2GV (1969-74 Vehicles)

Severe high gear lean surge can be corrected in 307 V8 engines using this carburetor by adding an internal baffle to the air cleaner housing. Details are given in the September 1971 GMC Service News Letter.

FAST IDLE CAM (CHOKE ROD)


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Fig. Fig. 29 Fast idle cam (choke rod) adjustment-2GV carburetors

  1. Turn the stop screw in until it contacts the bottom step of the fast idle cam, then turn it in one turn. Place the screw on the second step of the fast idle cam, 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


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Fig. Fig. 30 Choke vacuum break adjustment-2GV carburetors

  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 upper 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


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Fig. Fig. 31 Choke unloader adjustment-2GV carburetors

  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


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Fig. Fig. 32 Automatic choke coil rod adjustment-2GV carburetors

  1. Hold the choke valve completely open.
  2.  
  3. With the choke coil rod disconnected from the upper lever, push downward on the end 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


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Fig. Fig. 33 Accelerator pump rod adjustment-2GV and 2GC carburetors

  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 ring to the top of the pump rod.
  4.  
  5. Bend the pump rod at a lower angle to correct this dimension.
  6.  

FLOAT LEVEL


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Fig. Fig. 34 Float level adjustment (plastic float)-2GV and 2GC carburetors

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

On plastic 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


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Fig. Fig. 35 Float drop adjustment (brass float)-2GV carburetors

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

On plastic 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 surface to the bottom of the float.

Bend the float tang to adjust either type float.

Model 2GC (1975 and 1977-78 Vehicles)


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Fig. Fig. 36 Exploded view of the Rochester 2GC carburetor



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Fig. Fig. 37 Rochester 2GC carburetor component list

Any adjustments not illustrated for the 2GC are similar to those for the 2GV. Be sure to check the text against the illustration, since some gauge points will change.

ACCELERATOR PUMP ROD


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Fig. Fig. 38 Accelerator pump rod adjustment-2GV and 2GC carburetors

  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. It should be 1 5 / 8 inch for 1975 and 1 21 / 32 inch for 1977-78.
  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. It should be 0.400 inch for 1975 and 0.260 inch for 1977-78.
  4.  
  5. Bend the choke lever tang to adjust.
  6.  

CHOKE UNLOADER


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Fig. Fig. 39 Choke unloader adjustment-1977-78 2GC carburetors

  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. It should be 0.350 inch for 1975 and 0.325 inch for 1977-78.
  4.  
  5. Bend the throttle lever tang to adjust.
  6.  

AUTOMATIC CHOKE COIL


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Fig. Fig. 40 Automatic choke coil adjustment-2GC carburetors

  1. The engine must be cold.
  2.  
  3. Place the idle screw on the high step of the fast idle cam.
  4.  
  5. Loosen the thermostatic choke coil cover retaining screws.
  6.  
  7. 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. These are: centered for 1975 manual, and one notch rich for automatic.
  8.  
  9. Tighten the choke cover retaining screws.
  10.  

CHOKE VACUUM BREAK


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Fig. Fig. 41 Choke vacuum break adjustment-2GC carburetors

  1. Disconnect the vacuum house. 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 held inward.
  4.  
  5. Place the idle speed screw on the high step of the fast idle cam.
  6.  
  7. Hold the choke oil 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. It should be 0.130 inch when the vehicle is new, 0.160 inch after 22,500 miles.
  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


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Fig. Fig. 42 Float level adjustment (plastic float)-2GV and 2GC carburetors

These procedures are the same as for the model 2GV, covered earlier. Float level is 21 / 32 in. for 1975 and 19 / 32 inch for 1977-78. Float drop is 31 / 32 inch for 1975 and 1 9 / 32 inch for 1977-78.

Rochester 2SE (1979-82 Models)
FLOAT


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Fig. Fig. 43 Float adjustment-2SE carburetors

  1. Hold the float retainer in place with your hand and push the float down against the needle.
  2.  
  3. Place a 1 / 8 inch gauge for 1979 models, or 3 / 16 inch for 1980-82 models at the toe of the float.
  4.  
  5. Remove the float and bend the arm as necessary to adjust the level.
  6.  

FAST IDLE
  1. Refer to the underhood emissions sticker. Disconnect and plug any hoses indicated on the sticker.
  2.  
  3. Adjust the curb idle speed as outlined in Section Two.
  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.  

ELECTRIC CHOKE SETTING


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Fig. Fig. 44 Electric choke adjustment-2SE carburetors

  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


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Fig. Fig. 45 Air valve rod adjustment-2SE carburetors

  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 inch gauge between the rod and the end of the slot in the lever.
  6.  
  7. Bend the rod to obtain 0.040 inch clearance.
  8.  

FAST IDLE CAM CHOKE ROD


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Fig. Fig. 46 Fast idle cam adjustment-2SE carburetors

  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 closed, 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 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


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Fig. Fig. 47 Primary side vacuum break adjustment-2SE carburetors

  1. Refer to Steps 1-5 of the Fast Idle Cam Choke Rod Adjustment procedure.
  2.  
  3. Rotate the scale to place the specified degree opposite the pointer. Refer to the "Carburetor Specifications Chart."
  4.  
  5. Fully seat the choke vacuum diaphragm using an outside vacuum source.
  6.  
  7. Hold the choke valve toward the closed position by pushing on the intermediate choke lever.
  8.  
  9. Bend the vacuum break rod until the bubble is centered and remove the gauge.
  10.  

Rochester M2MC/ME (1979-82 Models)

All adjustments for this carburetor are the same as the Rochester M4MC with the following exceptions:

FAST IDLE SPEED


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Fig. Fig. 48 Fast idle speed adjustment-M2MC carburetors

  1. Place the transmission in Park or Neutral.
  2.  
  3. Refer to the vehicle emission label and position the cam follower on the cam as per label.
  4.  
  5. Disconnect and plug the vacuum hose at the EGR valve.
  6.  
  7. Turn the fast idle speed screw to obtain the fast idle speed listed on the emission sticker.
  8.  
  9. Connect the vacuum hose.
  10.  

AUTOMATIC CHOKE COIL


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Fig. Fig. 49 Automatic choke coil adjustment-M2MC carburetors

  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.
  8.  
  9. Tighten the retaining screws or replace the rivets (Use cover kit).
  10.  

There is no adjustment for Air Valve Spring or Rear Vacuum Break on the M2MC.

Model 4MV (Quadrajet)


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Fig. Fig. 50 Exploded view of the Rochester 4MV carburetor



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Fig. Fig. 51 Rochester 4MV carburetor component list

FAST IDLE SPEED


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Fig. Fig. 52 Fast idle speed adjustment-4MV carburetors

  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 1973-1974 models with manual transmission, 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)


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Fig. Fig. 53 Choke rod (fast idle cam) adjustment-4MV carburetors

  1. Place the cam follower on the second step of the fast idle cam against the high step.
  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 (upper starting 1975) edge of the choke valve and the inside air horn wall.
  6.  
  7. To adjust, bend the choke rod.
  8.  

VACUUM BREAK


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Fig. Fig. 54 Choke vacuum break adjustment-4MV carburetors

  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.
  4.  
  5. Turn the vacuum break lever counterclockwise toward the closed choke position. 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


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Fig. Fig. 55 Choke unloader adjustment-4MV carburetors

  1. Push upon the vacuum break lever to close the choke and fully open the throttle valves.
  2.  
  3. Measure the distance from the lower (upper starting 1975) edge 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


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Fig. Fig. 56 Automatic choke coil rod adjustment-4MV carburetors

  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 level.
  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 warmup 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 . Make sure that the fast idle cam follower is not resting on the fast idle cam.
  2.  
  3. There should be 0.020 inch 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. With two point linkage, the bottom of the link should be in the center of the secondary lever slot.
  4.  
  5. With the 1969 three point linkage, there should be 0.070 inch clearance between the link and the middle tang.
  6.  
  7. Bend the upper tang on the secondary lever to adjust as necessary.
  8.  

FLOAT LEVEL


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Fig. Fig. 57 Float level adjustment-4MV and M4MC carburetors

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. Measure at a point 3 / 16 inch back from the toe for all models except for 1973-76, which should be measured at a point 1 / 16 inch back.

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

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, if necessary.
  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/ME (1975 and 1977-82 Models)

Any adjustments not illustrated for the M4MC are similar to those for the 4MV. Be sure to check the text against the illustration, since some gauge points will change.

PUMP ROD


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Fig. Fig. 58 Pump rod adjustment-M4MC carburetors

  1. Take the fast idle cam follower off the fast idle cam steps.
  2.  
  3. Back out the ide 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 position, then readjust later.
  6.  
  7. Place the pump rod in the inner hole in the lever unless specified otherwise in the "Carburetor Specifications 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


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Fig. Fig. 59 Fast idle speed adjustment-M4MC carburetors

  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 three turns.
  6.  
  7. Check the fast idle speed, adjust by turning the screw.
  8.  

CHOKE COIL LEVER
  1. Loosen the three retaining screws or remove the rivets 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 inch 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.  

A "stat" cover retainer kit is necessary when reinstalling a riveted cover.

CHOKE ROD (FAST IDLE CAM)


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Fig. Fig. 60 Choke rod (fast idle cam) adjustment-M4MC carburetors

  1. Adjust the fast idle.
  2.  
  3. Place the cam follower on the second step of the fast idle cam firmly against the rise 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


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Fig. Fig. 61 Air valve dashpot adjustment-M4MC carburetors

  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 inch.
  6.  
  7. Bend the air valve dashpot rod to adjust the clearance.
  8.  

FRONT VACUUM BREAK


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Fig. Fig. 62 Front vacuum break adjustment-M4MC carburetors

  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


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Fig. Fig. 63 Rear vacuum break adjustment-M4MC carburetors

  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


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Fig. Fig. 64 Choke unloader adjustment-M4MC carburetors

  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 contacts 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


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Fig. Fig. 65 Air valve spring adjustment-M4MC carburetors

  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


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Fig. Fig. 66 Float level adjustment-4MV and M4MC carburetors

Use the procedure given earlier for the model 4MV, measuring at a point 3 / 16 inch from the toe of the float.

 
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