The pilot refuelled the aircraft to full tanks on the evening prior to the accident. The aircraft remained parked at Griffith aerodrome overnight. The next day, the pilot completed two tasks of 0.8 hours each. He then conferred with his chief pilot, about the fuel endurance of the aircraft, before commencing another 0.8 hour task. After a flight time of 0.7 hours, while completing the "clean-up" run, the engine stopped. The pilot completed the emergency checks but was unable to restore engine power. He was then faced with a forced landing in a rice paddock. During the landing roll, the aircraft struck a dirt bank which bent the landing gear and damaged the fuselage and hopper. The pilot was familiar with the fuel usage rate of the aircraft and planned on a rate of 100 litres per hour. The fuel capacity of the aircraft was 328 litres and at the expected usage rate should have allowed an endurance in excess of three hours. The pilot believes that the aircraft was tampered with overnight. The fuel contents were not checked prior to departure that morning.