System

Fig. 1 Exploded view of Motorcraft Model 740 carburetor. 1982-83 shown, 1984-85 similar:

The Motorcraft Model 740 carburetor, Fig. 1, consists of five basic systems: choke system, idle system, main metering system, acceleration system and power enrichment system.

The choke system is used for cold engine starting and consists of a bi-metallic spring and an electric heater. The idle system is adjustable and provides for the proper air/fuel ratio for both idle and low speed operation. The main metering system provides the correct air/fuel ratio for normal cruising speeds. A main metering system is used for primary and secondary stage operation. The acceleration system consists of a diaphragm type pump that is mechanically operated by the primary throttle linkage. This system provides fuel to the primary stage during acceleration. The power enrichment system consists of a vacuum operated power valve and a secondary stage pull over system that is regulated by airflow. This system is used together with the main metering system to provide proper vehicle operation during periods of moderate to heavy acceleration. The distributor and EGR vacuum ports are located in the primary venturi area of the carburetor.