Fuel supply control system for engine

In a fuel supply control system for an engine in which a valve housing is provided with a negative pressure working chamber, and a negative pressure responsive-type control valve operable to be opened and closed in response to generation and extinction of a negative pressure in the negative pressure working chamber, the control valve being incorporated into a fuel passage between a fuel tank and a carburetor, the negative pressure working chamber being in communication with a negative pressure generating section in the engine through a negative pressure conduit, an oil flow-out preventing device is provided in a connecting portion for connecting the negative pressure generating section and the negative pressure conduit to each other. The oil flow-out preventing device is adapted to cut off the communication between the negative pressure generating section and the negative pressure conduit by a lubricating oil received from the negative pressure generating section, when the engine is inclined at a given angle or more. Thus, in an operational attitude of the engine, the transmission of the negative pressure from the negative pressure generating section to the negative pressure conduit is not obstructed, and even when the engine is inclined at the given angle or more in an operation-stopped state of the engine, the lubricating oil in the engine can be prevented from flowing out toward the negative pressure conduit.