Carburetor - ROCHESTER E4MC/E4ME: Description

The E4MC and E4ME carburetors are of a 2-stage, downdraft design. Each bore has a triple venturi system. The secondary side 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 a float bowl-mounted heated air choke assembly; the E4ME, an electrically-actuated choke assembly. All E4MC and most E4ME models have 2 vacuum break diaphragm assemblies, the front and rear, while some E4ME models have only the front vacuum break assembly.

Both the E4MC and E4ME models are used in conjunction with the Computer Command Control (CCC) System. The carburetors are equipped with an electrically-actuated mixture control solenoid mounted in the float bowl. Fuel metering is controlled by stepped metering rods that operate in removable jets.

Both models include tamper-resistant factory settings of the mixture control solenoid rich mixture stop screw and lean mixture screw, idle air bleed valve, TPS, ILC, ISC, ISS and idle mixture screws. No attempt should be made to 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.

The 5.0L (VIN Y) engine is equipped with 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 engines may be equipped with an Idle Speed Control (ISC) on the fuel bowl. Controlled by the ECM, the ISC controls the normal curb idle speed and acts as a dashpot on deceleration and throttle closing. On vehicles without ILC or ISC, but with air conditioning, an Idle Speed Solenoid (ISS) maintains a specific idle speed during A/C operation.