PURPOSE: To prevent the output reduction of an engine by installing a wind shielding filter on the inlet side of the air vent of a carburetor, thus keeping the pressure difference between the float chamber of the carburetor and an intake passage high.

CONSTITUTION: A carburetor 6 has a fuel injection nozzle 14 penetrating from a float chamber 12 to an intake passage 13, and has an air vent 15 communicating to the atmosphere side from the float chamber 12. The fuel injection nozzle 14 jets out the fuel in the float chamber 12 into the intake passage 13 by the pressure difference between the float chamber 12 and the intake passage 13. The air vent 15 is equipped with a wind shielding filter 17 made of foamed urethane through a pipe 16 on the inlet side. The wind shielding filter 17 is supported and fixed at the position close to the wall surface of an engine 3. Though a negative pressure state is generated in front of an aeropropeller by the leading flow generated by the aeropropeller, said negative pressure is shielded by the wind shielding filter 17, and the pressure difference between the float chamber 12 and the intake passage 13 is not reduced, and therefore, the fuel injection quantity is not reduced, and the engine-output reduction is not generated.