To stabilize combustion condition, and suppress fluctuation of engine rotating speed by arranging an opening/closing valve on the way of a fuel passage, closing the opening/closing valve at least between a low speed region and an intermediate speed region in engine rotating speed, to put a power jet off.

In this carburetor 60 disposed in an engine for motorcycle, a power jet 60 is disposed. In the power jet 60, a fuel blow-out hole 62 connected to a fuel chamber 32 through a fuel passage 62 is opened to a venturi part 36, fuel is sucked by intake negative pressure in the venturi part 36 for a constant value or more, and it flows out from the fuel blow-out hole 62. In this case, an opening/closing valve 70 for closing the fuel passage 61 when the level of engine rotating speed is in a region between low speed and intermediate speed or when it is in an excessive rotating region, is attached to an upper position of an intermediate chamber 66 of a carburetor body 30. The opening/ closing valve 70 is composed of a solenoid valve. When the solenoid valve is turned on when the level of the engine speed is in a region between the low speed and the intermediate speed, and the power jet 60 is turned off so as to prevent fuel from flowing out.