On January 22, 2000, about 1430 Pacific standard time, an experimental Mince Jurka MJ77, N751JR, made a forced landing following a loss of engine power near Rio Vista, California. The commercial pilot/owner was operating the airplane under the provisions of 14 CFR Part 91. The pilot was not injured; the airplane sustained substantial damage. The personal cross-country flight departed Stockton, California, en route to Petaluma, California, about 1400. Visual meteorological conditions prevailed and no flight plan had been filed. The original incident classification was upgraded to an accident on February 1, 2000, based on assessment of the damage. The Federal Aviation Administration (FAA) accident coordinator interviewed the pilot. The pilot said the airplane was a 3/4 scale P-51 replica with a fuel injected automotive engine. The flight departed Stockton with full fuel onboard, which was 32 gallons of fuel in two 16-gallon tanks, and the engine burned about 14 gallons per hour. While cruising at 3,500 feet, the airplane gradually began to lose speed and altitude. The manifold pressure remained at a cruise setting, but the pilot felt the engine was not producing power. He switched fuel tanks from left to right, cycled the ignition switch, and adjusted the mixture. The engine coolant and oil temperature gauges remained in the green, but the power continued to decline. The pilot attempted to land in a plowed field with the landing gear down, but the landing gear separated from the airplane and damaged the wing spar. The pilot reported that in order to assist in the recovery, he drained all of the fuel out of the left fuel tank, and all but 5 gallons from the right tank the day after the accident. Investigators from the Safety Board and the FAA met with the pilot and examined the airplane on February 15. The pilot told them the engine had about 3 hours on it when he installed it in the airplane, and it now had about 60 hours on it. The recovery agent told them he drained 5 gallons of fuel from the right fuel tank and no fuel from the left tank. The fuel selector valve had been disconnected so he could not tell what position it was in. The fuel screen was clean and clear of debris; the fuel manifold distribution valve was clean and contained no fuel. The spark plugs were in good condition. The investigators connected a fuel supply to the engine and attempted to start the engine. After several attempts, they were able to start the engine and run it up to 3,000 rpm. They were not able to run it long because the water pump belt was broken and they couldn't get coolant to flow. The FAA accident coordinator talked to a shop owner in Stockton who said the airplane came in for an airshow in October, but had engine trouble. He rented the pilot shop space to work on the engine. He said the engine had a broken valve and the pilot repaired the engine himself. He said he advised the pilot to fly around the airport for an hour, but the pilot said he had run the engine on the ground for an hour and experienced no problems. The shop owner said he observed the takeoff and thought that the engine ran so rough that it could not become airborne. The accident coordinator talked to the two companies that sell fuel at the airport. One had no records of a fuel sale to this registration number. The other company verified that it refueled this airplane and the pilot's T-6 during the airshow with a combined total of 90 gallons and had no records of refueling it since that time.