Various carburetors have been available on Chevrolet full size cars since 1979. Before attempting to service a carburetor, some effort should be made to first determine the type and model of carburetor with which your vehicle is equipped. On some older vehicles, the carburetor may not be the same as original, but in recent years the use of electronic engine controls and feedback systems has complicated switching carburetors and discouraged this practice on newer vehicles. Unless the engine in your car has been substantially altered there is a very good chance that the original model or type carburetor is still being used on your vehicle.
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.
All carburetors used on these vehicles should be stamped with an identification code somewhere on the float bowl. Most models are stamped vertically, on the side of the bowl though this may vary with some models. Some examples of ID number locations are:
REMOVAL & INSTALLATION
- Disconnect the negative battery cable, then remove the air cleaner assembly and its gasket.
- Disconnect the fuel line from the carburetor, then tag and disconnect the vacuum lines.
- Disconnect the choke coil rod, heated air line tube, or electrical connector.
- Disconnect the throttle linkage, and if equipped, the cruise control linkage.
- If equipped disconnect the transmission throttle valve linkage.
- Disconnect the throttle return spring(s).
- Remove the CEC valve vacuum hose and electrical connector.
- If equipped, disconnect the EGR line.
- If equipped, remove the idle stop solenoid.
- Remove the carburetor attaching nuts and/or bolts, then remove the carburetor and gasket or insulator.
Immediately cover the opening in the intake manifold to prevent dirt, debris or even loose bolts from falling into the engine, necessitating manifold removal.
- If desired, fill the float bowl with gasoline before installing the carburetor. This will help ease starting the engine later.
- Remove the cover from the intake manifold, then install the carburetor using a new gasket or insulator and tighten the retaining bolts.
- If equipped, install the idle stop solenoid.
- If equipped, connect the EGR line.
- Install the CEC valve vacuum hose and electrical connector.
- Connect the throttle return spring(s).
- If equipped, connect the transmission throttle valve linkage.
- Connect the throttle linkage, and if equipped, the cruise control linkage.
- Connect the choke coil rod, heated air line tube, or electrical connector.
- Connect the vacuum lines as noted during removal, then connect the fuel line to the carburetor.
- Install the air cleaner assembly and gasket, then connect the negative battery cable.
- Start and run the engine, then check for leaks.
- Check and adjust the carburetor, as necessary.
Efficient carburetion depends greatly on careful cleaning and inspection during overhaul, since dirt, gum, water or varnish either in or on the carburetor parts are often responsible for poor performance. Always 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 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:
- Check the float needle and seat for wear. If wear is found, replace the complete assembly.
- Check the float hinge pin for wear and the float(s) for dents or distortion. Replace the float if fuel has leaked into it.
- 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.
Throttle shafts and bushings are not included in most overhaul kits. They can usually be purchased separately.
- 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.
- 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.
- Check the bowl cover for warped surfaces with a straightedge.
- Closely inspect the accelerator pump plunger for wear and damage, replacing as necessary.
- 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.
- After the carburetor is assembled, check the choke valve for freedom of operation.
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:
Major Repair 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.
The following should be observed before attempting any adjustments.
- Thoroughly warm the engine. If the engine is cold, be sure that it reaches operating temperature.
- 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 adjustments will inevitably lead to frustration.
- Check the manifold heat control valve (if used) to be sure that it is free.
- Check and adjust the choke as necessary.
- 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.
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.