The pilot was returning to his home airport from a four hour round-robin flight with on landing and takeoff en route. The fuel tanks were full at the first takeoff and no fuel had been added. The aircraft's fuel quantity at the time of the accident was calculated to be 25 gallons. The pilot reported he had lost the engine approximately 1/2 mile from the runway. A witness observed the aircraft's nose raise and the aircraft enter into a steep descending right turn before it collided with the ground. A post-crash engine operational test did not disclose any evidence of a failure or malfunction that would have resulted in an engine failure. The aircraft's right wing tank was ruptured during the impact sequence. The left tank was leaking and only 5 gallons of fuel was recovered. The position of the fuel selector handle in the cockpit pointed toward the right fuel tank. The fuel selector valve was found positioned between the off and left tank position when removed.