The pilot and his passengers were on the final stages of a trip through central and northern Australia. After spending the night at Clermont they were observed to enter the aircraft, and following engine start an engine run-up was carried out. Witnesses reported that at times during the run-up the engine ran roughly. Following the run-up, the pilot taxiied the aircraft to the runway threshold and the takeoff was commenced. During the takeoff run the engine sound was reported as being normal. The aircraft was then observed to become airborne and a short time later the sound of an impact was heard. The wreckage was located in timbered country, 475 metres beyond the upwind end of the departure runway. The investigation revealed that the No 3 cylinder exhaust valve had stuck shortly after takeoff, resulting in a substantial loss of engine power. The valve appears to have become jammed in the closed position due to a build up of carbon in the valve guide which resulted in the pushrod bending. Following the power loss the pilot was faced with carrying out a forced landing on unsuitable terrain.