Abstract: A diaphragm-type fuel pump defining therein an outlet chamber for supplying fuel to a carburetor. A return pipe is connected to the interior of the outlet chamber to permit return of vapors to the fuel tank. An outlet pipe communicates with the outlet chamber for supplying fuel to the carburetor float chamber. The fuel pump has an outlet valve associated therewith for supplying fuel into the outlet chamber. The open inlet end of the return pipe communicates with the outlet chamber at an elevation which is higher than the elevation of the outlet valve, and the inlet opening of the outlet pipe communicates with the outlet chamber at an elevation which is lower than the elevation of the outlet valve, whereby vapors within the outlet chamber are prevented from passing through the outlet pipe to the carburetor.