General Information

Carburetor Fuel Circuit Schematic:

The carburetor has a variable venturi, in which a piston maintains the air flow velocity through the the venturi at a nearly constant level by changing the cross-sectional area of the venturi according to the amount of intake air. When the air flow volume changes, the area between the main jet and the metering needle is altered by the in and out movement of the metering needle to create the appropriate air/fuel ratio. The amount of air that passes through the venturi changes according to the throttle valve opening and the engine rpm. As a result, the vacuum that is created at the venturi changes according to the air flow rate.

Vacuum at the venturi is transmitted through the suction hole to the suction chamber. The suction piston remains at a point where the force of the vacuum which tends to pull it, and the force of the spring which tends to push it, are balanced.

The main fuel system of the carburetor consists of the metering needle and main jet, which serves to supply fuel in appropriate amounts to match the overall driving conditions. The metering needle is tapered at one end and moves along with the suction piston, controlling the amount of fuel passing through the main jet by changing the size of the main jet opening. The fuel in the float chamber flows through the fuel inlet tube and the main jet controls the fuel flow rate.

The bypass fuel system is provided to supply additional fuel during idle. Fuel is drawn from the float chamber through the bypass jet and mixed with air from the air bypass bleeder, then sprayed out of the bypass port. The ratio of the air/fuel mixture is controlled by the idle mixture adjusting screw.