Abstract: A four cycle internal combustion engine including a secondary intake system. The secondary intake system includes a pumping diaphragm actuated by pressure variation within the engine crankcase. The pumping diaphragm is in turn connected to the intake passage through a secondary intake passage to receive and expel air/fuel mixture toward the intake valving at appropriate intervals. A control valve control communication between the crankcase and the pumping diaphragm to restrict or allow actuation of the pumping diaphragm. An outlet also extends from the system to vent the crankcase at appropriate intervals.