Carburetor: Description and Operation

Fig. 1 Upper body. Motorcraft 7200 VV:

Fig. 2 Throttle body. Motorcraft 7200 VV:

Fig. 3 Main body. Motorcraft 7200 VV:

The Motorcraft 7200VV variable venturi carburetor, Figs. 1 through 3, varies the area of the venturi according to engine speed and load. This is accomplished by dual venturi valves that are controlled by engine vacuum and throttle position. The position of the venturi valves changes according to engine demands to determine the area for air flow to the two throats of the carburetor. The venturi valves are connected to two tapered main metering rods that ride in the main metering jets. During operation, air speed through the carburetor is fairly constant, providing more even air/fuel mixtures throughout the engine operating range.

The carburetor varies the air/fuel ratio in response to commands from the EEC control module. The air bleed feedback system uses a stepper motor activated by a signal from the EEC module to regulate bleed air admitted into the main fuel metering system.

The stepper motor modulates the pintle movement in the metering orifice, varying the air bleed into the main system. The greater the amount of bleed air, the leaner the air/fuel mixture.