Incident Summary
According to the pilot, during a local flight while on a base leg, the engine began running rough. After turning final and applying power, the engine ran smoothly. The engine then alternated between rough and smooth operation. The pilot reported that the airplane contacted the ground short of the runway due to a loss of engine power. During the landing, a wing impacted a tree, and the airplane subsequently nosed over.
Wreckage Examination
Federal Aviation Administration Inspectors examined the wreckage. They discovered a brown, varnish-like substance seeping from the carburetor fuel line. No further pre-impact anomalies were detected during the examination.
Pilot Statement
The pilot stated that he used "automobile" gas in the aircraft and that "some fuel in the gas tank was left over from last year." He offered a safety recommendation: "I will never use other than fresh fuel [and] will completely drain old gas from tank at end of flying season."