PURPOSE: To keep the air-fuel ratio control range of mixed gas sent in an engine in accurate condition so as to prevent the deterioration of combustion of the engine, by automatically removing carbon, etc., adhering to the surface of the needle of a variable venturi type carburetor.

CONSTITUTION: As against a needle 13, which advances and retreats within the fuel supply port 12 opened in the venturi part 3a of an intake path 3, being fixed to the tip of a piston valve 7, a mobile member 20, which contacts with the periphery of the needle 13, being moved by the flow of the gas within the intake path 3, is retained by the venturi part 3a such that it surrounds the periphery of the needle 13 without blocking up the outlet of the fuel supply port 12.