All vehicles with the 5.8L engine are equipped with a Motorcraft 7200 Variable Venturi (VV) carburetor. Fuel is supplied to the carburetor by a mechanical fuel pump mounted on the engine. The fuel pump is driven by an eccentric attached to the front of the camshaft.
The 7200 VV carburetor is unique in that it is able to vary the venturi area according to engine speed and load, which is quite different from standard carburetors which have a fixed venturi area. The venturi area is varied by dual venturi valves that are controlled by engine vacuum and throttle position. The position of the venturi valves change, depending on engine demands, to determine the area for airflow 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. When the venturi valve position varies, the metering rods vary the fuel flow by changing the flow area of the main metering jets. During engine operation, air speed through the carburetor is fairly constant, causing more even air/fuel mixtures throughout the engine operating range.
In a traditional fixed venturi carburetor, airflow speed varies according to throttle opening and engine speed, making a supplementary idle system and power enrichment system necessary in order to work with the changing flow speed. In the variable venturi carburetor, these supplementary systems are not necessary.
The variable venturi carburetor varies the air/fuel ratio in response to signals from a control module. The air bleed feedback system used on the variable venturi carburetor uses a stepper motor, activated by a signal from the control 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 air/fuel mixture becomes leaner as the amount of air becomes greater.