To reduce the cost of the return mechanism of a circulation type carburetor by using a fuel tank for the circulation type carburetor and a fuel tank for the other carburetor in common, while the fuel tank for the circulation type carburetor requires an air layer above the tank so that a return pipe opening section is not dipped in fuel and the dedicated fuel tank was required in the past.

A grommet 34 is formed into a protruded shape and is protruded upward on a fuel tank 7, a cavity section 37 is formed in the grommet 34, and the tip of a return pipe is opened in the cavity section 37. When this grommet 34 is merely fitted to a grommet hole 33 formed on the shell of a fuel tank for the other carburetor, the fuel tank for the circulation type carburetor can be formed, and the shell of the fuel tank can be used in common for the circulation type carburetor and the other carburetor.