Carburetor - ROCHESTER E4MC/E4ME: Description: Notes

The E4MC and E4ME carburetors are of a 2-stage, downdraft design. The secondary circuit is composed of 2 large throttle bores, using the air valve principle, in which fuel is metered in direct proportion to the amount of air passing through the secondary throttle bores. A baffle is attached to the secondary side of the air horn, above the main well bleed tubes. This deflects incoming air to improve secondary nozzle operation on heavy acceleration.

The E4MC carburetor uses an air heated choke assembly; the E4ME, an electrically-actuated choke assembly. All E4MC and most E4ME models have 2 vacuum break diaphragm assemblies, primary and secondary, while some E4ME models have only primary vacuum break assembly.

Both the E4MC and E4ME models are used in conjunction with the Computer Command Control (CCC) system on General Motors vehicles. All carburetors are equipped with an electrically-actuated mixture control solenoid mounted in the float bowl. For all applications, fuel metering is controlled by stepped metering rods that operate in removable jets.

All models include tamper-resistant factory settings of the mixture control solenoid rich limit stop and lean mixture screw, idle air bleed valve, TPS, ILC, ISS and idle mixture screws. DO NOT  adjust these except during major overhaul or replacement of air horn, float bowl or throttle body. Both electric and hot air chokes have riveted covers which must not be removed except for major overhaul.

Some General Motors engines equipped with A/C use an Idle Load Compensator (ILC) attached to the fuel bowl. The ILC adjusts curb idle speed by sensing changes in manifold vacuum (engine load). To prevent the ILC from reacting too quickly to vacuum changes, a differential Vacuum Delay Valve (DVDV) is installed between the ILC and vacuum source. The DVDV delays operation of the ILC until vacuum change is constant.

All other General Motors engines are equipped with an ISS on the fuel bowl. Controlled by the ECM, the ISS controls the normal curb idle speed and acts as a dashpot on deceleration at speeds above 40 MPH. When equipped with A/C, the ISS maintains a specific idle speed during A/C compressor operation.