PATH:Fuel SystemCarbureted Fuel SystemCarburetorsOverhaulRochester Carburetors / Print
Rochester Carburetors

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 disassemble, 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. Check the float hinge pin for wear and the float(s) for dents or distortion. Replace the float if fuel has leaked into it.
  3. 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 it; wear may allow air leakage, which could affect starting and idling.

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. 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 moisture.
  3. Check the bowl cover for warped surfaces with a straightedge.
  4. Closely inspect the valves and seats for wear and damage, replacing as necessary.
  5. 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 supplies 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.

Model E4ME carburetor
Click to Enlarge
Model E4ME carburetor parts identification
Click to Enlarge
Model M4MC/M4ME carburetor
Click to Enlarge
Model M4MC/M4ME carburetor parts identification
Click to Enlarge
Model M4MEF carburetor
Click to Enlarge
Model M4MEF carburetor parts identification
Click to Enlarge
PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRemoval & InstallationModel E4 Series Carburetors / Print
Model E4 Series Carburetors
WARNING
Before removing the carburetor allow the engine to cool completely to prevent ignition and possible fire from hot engine components such as the exhaust manifold.
  1. Disconnect the negative battery cable.
  2. Remove the air cleaner and its gasket.
  3. Disconnect the fuel and vacuum lines from the carburetor.

WARNING
Keep a rag handy to soak up any gasoline that might spill on any other components. Immediately dispose of the rag in a container approved for flammable or combustible refuse.
  1. Disconnect the electrical connectors for the choke and idle solenoid.
  2. Disconnect the throttle linkage. Also disconnect the cruise control and transmission linkage, if equipped.
  3. Remove the carburetor attaching bolts, gasket or insulator, and remove the carburetor.

To install:

  1. Install new heat shield and insulator gaskets to the intake manifold.
  2. Install the carburetor with the float bowl filled with gasoline to ease starting the engine later. Tighten short bolts to 11 ft. lbs. (15 Nm) and long bolts to 7 ft. lbs. (9 Nm).
  3. Reconnect the throttle linkage. Also reconnect the cruise and transmission linkage if so equipped.
  4. Reconnect the electrical connectors for the choke and idle solenoid.
  5. Reconnect the fuel and vacuum lines from the carburetor.
  6. Reconnect the negative battery cable.
  7. Check for fuel leaks by cranking the engine a little but not starting it. Be sure to check not only at the carburetor fuel line fitting but also at the fuel pump.
  8. Install the air cleaner and its gasket.

With the bolts removed carefully lift the carburetor from the intake manifold
Click to Enlarge
Remove the gasket from the intake manifold
Click to Enlarge
If the carburetor is to be removed for any length of time, use a rag or some paper towels to cover the intake manifold opening
Click to Enlarge
PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRemoval & InstallationModel M4 Series Carburetors / Print
Model M4 Series Carburetors
WARNING
Before removing the carburetor allow the engine to cool completely to prevent ignition and possible fire from hot engine components such as the exhaust manifold.
  1. Disconnect the negative battery cable.
  2. Remove the air cleaner and its gasket.
  3. Disconnect the fuel and vacuum lines from the carburetor.

WARNING
Keep a rag handy to soak up any gasoline that might spill on any other components. Immediately dispose of the rag in a container approved for flammable or combustible refuse.
  1. Disconnect the electrical connectors for the choke and idle solenoid.
  2. Disconnect the throttle linkage. Also disconnect the cruise control and transmission linkage, if equipped.
  3. Remove the carburetor attaching nuts and/or bolts, gasket or insulator, and remove the carburetor.

To install:

  1. Install new heat shield and insulator gaskets to the intake manifold.
  2. Install the carburetor with the float bowl filled with gasoline to ease starting the engine later. Tighten in a criss-cross pattern to 144 inch lbs. (16 Nm).
  3. Reconnect the throttle linkage. Also reconnect the cruise and transmission linkage, if so equipped.
  4. Reconnect the electrical connectors for the choke and idle solenoid.
  5. Reconnect the fuel and vacuum lines from the carburetor.
  6. Reconnect the negative battery cable.
  7. Check for fuel leaks by cranking the engine a little but not starting it. Be sure to check not only at the carburetor fuel line fitting but also at the fuel pump.
  8. Install the air cleaner and its gasket.

Loosen the carburetor retaining bolts either using a ratchet or a wrench
Click to Enlarge
At one end of most carburetors are 2 long retaining bolts
Click to Enlarge
Shorter carburetor retaining bolts may be found at the base flange
Click to Enlarge
PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRochester E4me & E4mc Quadrajet / Print

Rochester E4me & E4mc Quadrajet

These 4-bbl carburetors feature an electrically operated mixture control solenoid, and are designed as part of the GM Computer Command Control (C3) system. As with the E2SE 2-bbl, the electric mixture control solenoid is mounted in the float bowl, and is used to control the air/fuel mixture in the primary bores of the carburetor. The plunger in the solenoid is controlled, or pulsed, by electrical signals received from the Electronic Control Module (ECM).

An Idle Speed Control (ISC) assembly, monitored by the ECM, controls engine idle speed. The curb (base) idle is programmed into the ECM and is not adjustable. When the throttle lever is resting against the ISC plunger, the ISC acts as a dashpot on throttle closing. An Idle Speed Solenoid or Idle Load Compensator is used on some models to position the primary throttle valve, providing engine idle speed requirements.

On E4MC models, an Idle Load Compensator (ILC) mounted on the float bowl is used to control curb idle speeds. The ILC used manifold vacuum to sense changes in engine load (the A/C compressor clutch engaged, for example) and compensates by adjusting throttle angle for the curb idle speed. The ILC uses a spring loaded vacuum-sensitive diaphragm whose plunger either extends (vacuum decrease) or retracts (vacuum increase) to adjust throttle angle for curb idle speeds. Both the ISC and ILC are factory adjusted.

PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRochester E4me & E4mc QuadrajetAccelerator Pump / Print
Accelerator Pump

The accelerator pump is not adjustable on computer controlled carburetors (E4MC and E4ME).

  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. Bend the secondary throttle closing tang away from the primary throttle lever, if necessary, to insure that the primary throttle valves are fully closed.
  3. With the pump in the appropriate hole in the pump lever, measure from the top of the choke valve wall to the top of the pump stem.
  4. To adjust, bend the pump lever.
  5. After adjusting, readjust the secondary throttle tang and the slow idle screw.

E4ME/MC Accelerator pump adjustment
Click to Enlarge
E4ME/MC Fast idle adjustment
Click to Enlarge
E4ME/MC Front vacuum break adjustment
Click to Enlarge
E4ME/MC Rear vacuum break adjustment
Click to Enlarge
PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRochester E4me & E4mc QuadrajetFloat Level / Print
Float Level

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 (1/16 in. back from the toe).

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

Remove the float and bend the float arm to adjust except on carburetors used with the computer controlled systems (E4MC and E4ME). For those carburetors, if the float level is too high, hold the retainer firmly in place and push down on the center of the float to adjust. If the float level is too low on models with the computer controlled system, lift out the metering rods. Remove the solenoid connector screw. Turn the lean mixture solenoid screw in clockwise, counting and recording the exact number of turns until the screw is lightly bottomed in the bowl. Then turn the screw out clockwise and remove. Lift out the solenoid and connector. Remove the float and bend the arm up to adjust. Install the parts, turning the mixture solenoid screw in until it is lightly bottomed, then unscrewing it the exact number of turns counted earlier.

E4ME/MC float level adjustment
Click to Enlarge

Top of Form

PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRochester M4me, E4me, E4mc 4-Bbl Carburetors / Print

Rochester M4me, E4me, E4mc 4-Bbl Carburetors

For carburetor adjustments for the 1980-87 M4ME/M4MC Rochester carburetor, please refer to the following illustrations.

M4ME and M4MC float adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC pump adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC air valve spring adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC choke coil lever adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC choke valve angle gauge adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC choke rod fast idle cam adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC vacuum break adjustment information, 1980 and later
Click to Enlarge
M4ME and M4MC front vacuum break adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC rear vacuum break adjustment, 1980 and later
Click to Enlarge
M4ME and M4MC air valve rod adjustment (front), 1980 and later
Click to Enlarge
M4ME and M4MC air valve rod adjustment (rear), 1980 and later
Click to Enlarge
M4ME and M4MC unloader adjustment, 1980 and later
Click to Enlarge

§  Air Valve Rod Adjustment

§  Choke Coil Lever Adjustment

§  Electric Choke Setting

§  Fast Idle Adjustment

§  Float Level Adjustment

§  Primary Side Vacuum Break Adjustment

§  Pump Adjustment

Bottom of Form

PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRochester M4me, E4me, E4mc 4-Bbl CarburetorsAir Valve Rod Adjustment / Print
Air Valve Rod Adjustment

Refer to the accompanying illustration for this procedure.

E2SE 2-bbl. air valve rod adjustment
Click to Enlarge
PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRochester M4me, E4me, E4mc 4-Bbl CarburetorsChoke Coil Lever Adjustment / Print
Choke Coil Lever Adjustment
  1. Remove the three retaining screws and remove the choke cover and coil. On models with a riveted choke cover, drill out the three rivets and remove the cover and choke coil.

A choke cover retainer kit is required for reassembly.

  1. Place the fast idle screw on the high step of the cam.
  2. Close the choke by pushing in on the intermediate choke lever. On front wheel drive models, the intermediate choke lever is behind the choke vacuum diaphragm.
  3. Insert a drill or gauge of the specified size into the hole in the choke housing. The choke lever in the housing should be up against the side of the gauge.
  4. If the lever does not just touch the gauge, bend the intermediate choke rod to adjust.

E2SE 2-bbl. choke coil lever adjustment
Click to Enlarge
PATH:Fuel SystemCarbureted Fuel SystemCarburetorsRochester M4me, E4me, E4mc 4-Bbl CarburetorsElectric Choke Setting / Print
Electric Choke Setting

This procedure is only for those carburetors with choke covers retained by screws. Riveted choke covers are preset and nonadjustable.