On May 7, 2004, approximately 1230 mountain daylight time, a Crimmins Smyth Sidewinder, N92AC, operated by the pilot, was substantially damaged during a forced landing following a loss of engine power 1 mile east of Natrona, Wyoming. The commercial pilot, the sole occupant on board, was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the ferry flight being conducted under Title 14 CFR Part 91. The flight originated at Thermopolis, Wyoming, approximately 1130, and was en route to Aurora, Colorado, with a planned refueling stop in Casper, Wyoming. In his accident report, the pilot stated that he had just purchased the airplane and was ferrying it to his home base. He had flown the airplane for a total of 5 hours (3.5 hours the day before the accident, and 1.5 hours on the day of the accident) with the previous owner. After refueling the airplane to capacity, the pilot departed Thermopolis Airport (THP) at approximately 1130, en route to Casper, Wyoming. While in cruise flight at 9,500 feet msl, the engine --- which had been producing 2,500 rpm --- began "surging" and started losing power. Carburetor heat was opened and the mixture was adjusted, but the engine continued to lose power. The pilot said the cylinder head temperature, oil temperature, and oil pressure indicated normal parameters. As the airplane began losing altitude, the pilot decided to land in a field. During the landing rollout, the nose and right main landing gears were torn off, and the left main landing gear folded underneath the airplane. The firewall was buckled and both wings were crushed. According to the airplane maintenance records, the airplane was given a conditional inspection and found to be in an airworthy condition on May 6, 2004, at a tachometer reading of 596.6 hours. Prior to that, the last conditional inspection was on August 1, 1996, at a tachometer reading of 417.7 hours. Tachometer time between these two inspections was 178.9 hours. At the last conditional inspection, the fuel tank was removed, cleaned by a radiator shop, and reinstalled in the airplane. On June 23, 2004, the airplane was examined at Beegles Aircraft Service in Greeley, Colorado. The fuel line between the fuel selector valve and the gascolator was removed and examined. No obstructions were noted. When the fuel selector valve was removed from the fuel tank, approximately 1-2 quarts of fuel poured out. Examination of the fuel selector (which the pilot had placed in the OFF position after the accident) revealed a considerable amount of fine grit inside the fuel screen. Similar grit was seen inside the fuel tank.