The pilot was using his aircraft for agricultural operations on his own land. The aircraft had been performing normally during the day, however on this particular take-off the engine lost power when the aircraft had reached about 55 knots. There was insufficient strip length remaining for the pilot to stop the aircraft, which struck several fences before coming to rest in a ditch 50 metres beyond the end of the strip. Despite an extensive examination of the engine and associated systems, the reason for the power loss could not be determined. However, several months later the engine again failed during a take-off run. The fuel valve was dismantled, and it was found that rivets holding a teflon insert in place had corroded and fallen off. Corrosion products had then jammed the insert in a position where fuel flow was reduced by about 25 percent. A backing plate had also become dislodged and was free to move around the fuel valve. It was probable that this plate had blocked off the fuel supply to the engine during the attempted take-off.