On June 23, 2008, approximately 1910 central daylight time, an Air Tractor AT-502B, N5005G, was substantially damaged upon collision with terrain following a partial loss of power during initial takeoff from Bethany Memorial Airport(75K), Bethany, Missouri. Visual meteorological conditions prevailed at the time of the accident. The aerial application flight was being conducted under the provisions of Title 14 Code of Federal Regulations (CFR) Part 137 without a filght plan. The commercial pilot was not injured. The local flight was originating at the time of the accident. The accident pilot stated that another pilot told him the engine was not responding properly. In order to see how the engine was performing, the accident pilot decided to fly the airplane. After loading approximately 430 gallons of applicant, the pilot began his takeoff roll. At approximately mid-field the airplane's tail wheel raised up, but at approximately 560 feet of runway remaining, the engine began "rolling back." The pilot raised the nose of the airplane at the departure end and cleared the airfield fence before settling back to the ground. The airplane continued to travel through a field towards a residence when the engine momentarily regained power. The airplane collided with a garage and a residence, rolled inverted and slid 50 yard before coming to rest. The engine was removed and shipped to Pratt & Whitney Canada. Under the supervision of the Transportation Safety Board of Canada (TSB), an engine examination revealed that the engine displayed signs of rotation at the time of impact. An examination of the accessories revealed the fuel control unit (FCU) bellows was found with deformation consistent with power reduction and erratic engine performance in the high power range. Furthermore, an adjustment was noted to the FCU lever adjustment indicating possible maintenance corrections for low power. The FCU installed on the engine was found to be impact damaged and could not be tested. An examination conducted on the FCU bellows was conducted by Honeywell under the supervision of the FAA; no anomalies were detected in the FCU bellows. The bellows was returned to Pratt & Whitney Canada and, under the supervision of the TSB, was tested in a "slave" FCU with no anomalies detected.