Incident Summary
Approximately two hours and fifteen minutes into the flight, the engine began to run rough and lose power. Initially, engine RPM dropped by about 75 RPM. As power continued to decrease, the pilot performed several troubleshooting steps. The pilot checked both magnetos, turned the carburetor heat ON, and verified the fuel selector was in the Both position. The primer was ensured to be in, and the mixture was set to full rich, throttle to full open, and boost pump to ON.
Descent and Impact
Once engine power had decayed to approximately 1,900 RPM, the pilot initiated a descent to maintain airspeed. About 1,500 feet above ground level, the engine completely lost power. The airplane subsequently impacted a tree and came to a stop.
Engine Examination
Examination of the engine revealed that all valves were fouled with a glass-like material. The material was composed mostly of bromine and lead. The source of this material could not be determined.