Carburetor - ROCHESTER M4M Series 4-Bbl: Description

The M4M-series carburetors are all 4-barrel, two-stage carburetors. The primary side has a triple venturi system. The secondary side is composed of 2 large bores using the air valve principle (fuel is metered in direct proportion to amount of air passing through secondary bores). All models use an electric choke.

The General Motors M4MEF carburetor has adjustable wide open throttle mixture control. During wide open throttle conditions a factory-set secondary air bleed adjusting screw provides more precise control of the air/fuel mixture.

A dual capacity accelerator pump valve assembly, mounted in the float bowl, is used on General Motors M4MED carburetors. A dual capacity pump solenoid is also used.

When the engine is cold, more fuel is necessary to ensure a smooth transition from idle to part throttle. When the engine is warm, less fuel is needed. A coolant temperature sensor energizes a pump solenoid when coolant temperature exceeds 170°F (77°C). This solenoid opens the dual capacity pump valve, reducing pump capacity by about one-half.