An auxiliary chamber capable of changing its volume within a given range is provided separately from a fuel tank. The auxiliary chamber and a float chamber of a carburetor are communicated with each other. Fuel in the float chamber is sucked and temporarily evacuated, as needed, by increasing the volume of the auxiliary chamber, and the temporarily evacuated fuel is returned into the float chamber, as needed, by decreasing the volume of the auxiliary chamber. This prevents fixation of a carburetor due to residual fuel.

An auxiliary chamber capable of changing its volume within a given range is provided separately from a fuel tank. The auxiliary chamber and a float chamber of a carburetor are communicated with each other. Fuel in the float chamber is sucked and temporarily evacuated, as needed, by increasing the volume of the auxiliary chamber, and the temporarily evacuated fuel is returned into the float chamber, as needed, by decreasing the volume of the auxiliary chamber. This prevents fixation of a carburetor due to residual fuel.