Carburetor: Description and Operation

Fig. 2 Exploded view of Rochester Dual-Jet model E2M carburetor:

The dual jet carburetor, Fig. 2, is a two barrel, single stage unit, incorporating the design features of the primary side of the Quadrajet (four barrel) carburetor. These E2M carburetors are used with the Computer Controlled Catalytic Converter (C4) System or the Computer Command Control (C3) System. The triple venturi stack, plus small bores, results in precise fuel metering control during all periods of engine operation.
The main metering system has a separate main well for each main nozzle for good fuel flow through the venturi. An electrically operated mixture control solenoid, mounted in the fuel bowl, is used to control the fuel/air mixture metered to the idle and main metering systems. Fuel metering is controlled by two stepped metering rods positioned by a plunger in the mixture control solenoid. The solenoid plunger is controlled by an electric output signal from the Electronic Control Module (ECM). The ECM, responding from a signal from the Oxygen Sensor, energizes the solenoid to move the plunger and metering rods to control fuel delivery to the idle and main metering systems. At the same time, air metering to the idle system is controlled by an idle air bleed valve, located in the air horn, which follows the movement of the mixture control solenoid plunger to control the amount of air bleed into the idle system, to lean or enrich the mixture. The movement or cycling of the solenoid plunger occurs approximately ten times per second, thereby controlling the fuel/air mixture to achieving optimum mixture ratios.
On some units, an idle speed control (ISC), located on the float bowl, is used to control idle speed. On these units, the curb idle speed is programmed and controlled by the ECM.