PURPOSE: To improve distributing property and combustion of mixture in idling after the completion of warming up an engine by providing a shut-off valve in a fuel vapor path communicating to a fuel heating chamber and an idle port.

CONSTITUTION: An idle port 18 opened to an intake path 5 communicates to a float chamber 10 through a slow fuel path 19 while communicating to a fuel heating chamber 22 mounted on an exhaust manifold 4 through fuel vapor paths 26, 28 having a shut-off valve 27. A diaphragm chamber 33 in the valve 27 is connected an intake manifold 3 through a water temperature sensing valve 36 and others of an engine 1 so that the valve 36 is opened when cooling water temperature of the engine 1 reaches at least a set value. Thus, the valves 36, 27 are closed to supply liquid fuel in the chamber 10 to the port 18 when said temperature is cold, and the valves 36, 27 are opened after the completion of warming up the engine so that fuel vapor produced in the chamber 22 is sucked from the port 18 into the path 5 through the paths 26, 28.