PURPOSE: To stabilize the air/fuel ratio over a wide range from warm-up operation to a high temperature state by controlling an amount of fuel led to a fuel level gauge section of a variable venturi carburetor in accordance with an engine temperature and the value of an air/fuel ratio.

CONSTITUTION: A float chamber 1 is communicated with a chamber 4 via a variable throttle valve 12, and chamber 4 is isolated from a pressure control chamber 5 by means of a diaphragm 6. A fuel passage 7 is installed in communication with chamber 4, and the far end of passage 7 is opened to a venturi section 11 through a fuel level gauge section 8 constituted in combination with a needle 13a actuated by a suction piston 13. Further, the pressure control chamber 5 is communicated via a passage 9a and a variable throttle valve 9 with the upstream location of venturi section 11, and also communicated with venturi section 11 via a passage 10a and a fixed throttle valve 10. Variable throttle valve 9 is controlled via a control circuit 106 with outputs of an O2 sensor and the engine temperature sensor installed in an exhaust system.