NTSB Probable Cause

INADVERTENT STALL BY THE PILOT WHILE ATTEMPTING TO RETURN TO THE AIRPORT FOLLOWING LOSS OF ENGINE POWER. CONTRIBUTING TO THE ACCIDENT WAS THE LOSS OF POWER DUE TO A STICKING EXHAUST VALVE, AND FAILURE OF THE PILOT TO ASSURE ALL IGNITION LEADS WERE CONNECTED AND TIGHTENED BEFORE THE FLIGHT.