To eliminate the leak of air or fuel from a throttle hole of a throttle valve to a pin hole of a needle for adjusting the opening of a fuel nozzle hole of a fuel feed pipe.

The cylindrical throttle valve 39 having the throttle hole 49 is inserted in a valve chamber 35 crossed to an air-fuel mixture passage 25 laterally extending through a carburetor body 34. The needle 37 extending from the upper end of the throttle valve 39 is fitted to the fuel feed pipe 20 protruded from a fuel chamber 47 in the lower part of the carburetor body 34 to the throttle hole 40. The opening of the throttle hole 40 to the air-fuel mixture passage 25 is adjusted by the rotation of the throttle valve 39, and the opening of the fuel nozzle hole 38 of the fuel feed pipe 20 is adjusted by rising the falling the throttle valve 39. An elastic seal member 66 is fitted to a part in contact with the throttle hole 40 of the pin hole 65 for supporting the needle 37 of the throttle valve 39.