GM Chevy Mid-Size Cars 1964-1988 Repair Guide

Carburetors

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Since their introduction in 1964, mid-size Chevrolets have been factory equipped with at least nineteen different carburetors:



Carter AFB 4 bbl - 1964-65
 
Carter WCFB 4-bbl - 1964-65
 
Carter YF 1-bbl - 1966-67
 
Carter AVS 4-bbl - 1966
 
Holley 4150 4-bbl - 1965-70
 
Holley 4160 4-bbl - 1966-71
 
Rochester BV 1-bbl - 1964-67
 
Rochester MV 1-bbl - 1968-71
 
Rochester ME 1-bbl - 1977-79
 
Rochester 2GV 2-bbl - 1968-74
 
Rochester 2GC 2-bbl - 1975-79
 
Rochester M2ME 2-bbl - 1980
 
Rochester E2ME 2-bbl - 1980 and later
 
Rochester 4GC 4-bbl - 1964-66
 
Rochester 4MV 4-bbl - 1967-74
 
Rochester M4MC 4-bbl - 1975-77
 
Rochester 4MC 4-bbl - 1977-79
 
Rochester M4ME 4-bbl - 1980
 
Rochester E4ME 4-bbl - 1980 and later
 

MODEL IDENTIFICATION



See Figure 1

General Motors Rochester carburetors are identified by their model code. The first number indicates the number of barrels, while one of the last letters indicates the type of choke used. Possible codes include V for the manifold mounted choke coil, C for the choke coil mounted in the carburetor body, and E for electric choke, also mounted on the carburetor. Model codes ending in A indicate an altitude compensating carburetor.



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Fig. Fig. 1: Carburetor ID location

REMOVAL & INSTALLATION



See Figures 2, 3, 4, 5, 6, 7 and 8

All Carburetors
  1. Disconnect the negative battery cable, then remove the air cleaner assembly and its gasket.
  2.  
  3. Disconnect the fuel line from the carburetor, then tag and disconnect the vacuum lines.
  4.  
  5. Disconnect the choke coil rod, heated air line tube, or electrical connector.
  6.  
  7. Disconnect the throttle linkage, and if equipped, the Cruise Control linkage.
  8.  
  9. On automatic transmission vehicles, disconnect the throttle valve linkage if equipped.
  10.  
  11. Disconnect the throttle return spring(s).
  12.  
  13. If CEC equipped, remove the CEC valve vacuum hose and electrical connector.
  14.  
  15. If equipped, disconnect the EGR line.
  16.  
  17. If equipped, remove the idle stop solenoid.
  18.  
  19. Remove the carburetor attaching nuts and/or bolts, then remove the carburetor and gasket or insulator.
  20.  

Immediately cover the opening in the intake manifold to prevent dirt, debris or even loose bolts from falling into the engine, necessitating manifold removal.

To install:
  1. If desired, fill the float bowl with gasoline before installing the carburetor. This will help ease starting the engine later.
  2.  
  3. Remove the cover from the intake manifold, then install the carburetor using a new gasket or insulator and tighten the retaining bolts.
  4.  
  5. If equipped, install the idle stop solenoid.
  6.  
  7. If equipped, connect the EGR line.
  8.  
  9. If CEC equipped, install the CEC valve vacuum hose and electrical connector.
  10.  
  11. Connect the throttle return spring(s).
  12.  
  13. On automatic transmission vehicles, connect the throttle valve linkage, if equipped.
  14.  
  15. Connect the throttle linkage, and if equipped, the Cruise Control linkage.
  16.  
  17. Connect the choke coil rod, heated air line tube, or electrical connector.
  18.  
  19. Connect the vacuum lines as noted during removal, then connect the fuel line to the carburetor.
  20.  
  21. Install the air cleaner assembly and gasket, then connect the negative battery cable.
  22.  
  23. Start and run the engine, then check for leaks.
  24.  
  25. Check and adjust the carburetor, as necessary.
  26.  



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Fig. Fig. 2: Disconnect the fuel line from the carburetor



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Fig. Fig. 3: Tag all hoses and vacuum lines which must be disconnected to assure ease of assembly



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Fig. Fig. 4: Disconnect the throttle, Cruise Control and automatic transmission linkage, as applicable



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Fig. Fig. 5: Disconnect the throttle return springs



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Fig. Fig. 6: Use a ratchet and long extension to loosen the flange lower mounting bolts



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Fig. Fig. 7: Loosen the upper carburetor mounting bolts



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Fig. Fig. 8: Lift the carburetor and gasket or insulator from the intake manifold

OVERHAUL



All Types

See Figures 9 and 10

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. Always overhaul your carburetor in a clean, dustfree area. Carefully disassemble the carburetor, referring often to the exploded views and directions packaged with the rebuilding kit. Keep 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 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 and, if 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 most overhaul kits. They can usually 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 check ball and spring as necessary. If the valve is satisfactory wash the valve parts again to remove breath moisture.
  4.  
  5. Check the bowl cover for warped surfaces with a straightedge.
  6.  
  7. Closely inspect the accelerator pump plunger for wear and damage, replacing as necessary.
  8.  
  9. During assembly, pay close attention to torque specifications or sequences, when provided. If no sequence is provided, it is usually a good idea to start and the center of the component and gradually work outwards.
  10.  
  11. After the carburetor is assembled, check the choke valve for freedom of operation.
  12.  

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 diagrams
 
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
 



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Fig. Fig. 9: Example of air horn fastener tightening sequence-M4MC shown



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Fig. Fig. 10: Another air horn fastener tightening sequence-M2MC carburetor

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.

PRELIMINARY CHECKS (ALL CARBURETORS)



See Figures 11 and 12

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 and assembly screws. 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 the mixture screws are capped, don't adjust them unless all other causes of rough idle have been eliminated. If any other adjustments are performed that might possibly change the idle speed or mixture, adjust the idle and mixture again when you are finished with the other engine adjustments.
  10.  

Before you make any carburetor adjustments make sure that the engine is in tune. Many problems which are thought to be carburetor related can be traced to an engine which is simply out-of-tune. Any trouble in these areas will have symptoms like those of carburetor problems.



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Fig. Fig. 11: Check the carburetor when the engine is fully closed, the choke should be closed



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Fig. Fig. 12: Check the carburetor again when the engine has been fully warmed, the carburetor choke should open

 
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