Variable venturi type carburetor

摘要

A variable venturi type carburetor is provided having a vacuum generated in the venturi portion in accordance with the throttle valve opening. The vacuum is transmitted into a suction chamber through a vacuum passage so as to balance the force which is the sum of the force exerted by a suction spring and the force exerted by the atmospheric pressure introduced from an atmospheric pressure chamber. The suction piston is set to provide a cross-sectional area of the venturi portion corresponding to the intake air flow rate. The suction piston is provided with a guide groove receiving a guide roller which is rotatably mounted on a guide pin provided on the carburetor casing to oppose to the guide groove. The guide roller is adapted to roll along the guide groove to smooth the movement of the suction piston and prevents the suction piston from being rotated. The combination of the guide roller and the guide groove is free from the problem of wear, even after a long use, so as to ensure an extremely small hysteresis of behaviour of the suction piston and hence a highly accurate adjustment of the air fuel ratio. A suction spring is fixed at its both ends to the suction piston and the suction chamber in a twisted condition so as to bias the suction piston in a circumferential or rotational direction.