Incident Summary
The pilot reported that during the flight, the right fuel tank was used until empty, at which point the left tank was selected. Approximately 20 minutes after switching tanks and 2 hours 35 minutes after departure, the engine backfired and subsequently quit. A forced landing was made, during which the aircraft nosed down after contacting a sand dome.
Investigation Findings
Investigation revealed that during the 4 months the pilot owned the aircraft, he had to have the fuel system cleaned twice because of sediment. Inspection of the aircraft disclosed sediment in the fuel pumps and saddle tanks. The sediment was cleaned out, and the engine would not run longer than approximately 2 minutes on either tank. The fuel system was thoroughly checked, and the only discrepancy noted was excessive play in the fuel selector valve.