On May 18, 2000, about 1755 mountain daylight time, a Cessna 150G, N3054S, registered to and operated by Hinkle Aviation as a 14 CFR Part 91 instructional flight, nosed over in a field located four miles northeast of Middleton, Idaho. Visual meteorological conditions prevailed at the time and no flight plan was filed. The airplane was substantially damaged. The flight instructor was not injured and the student pilot received minor injuries. The flight originated from Caldwell, Idaho, about one hour prior to the accident. In a written statement, the flight instructor reported that while returning to Caldwell at 3,500 feet mean sea level, the engine suddenly lost power. The pilot attempted to isolate the problem and found that by priming, he was able to get momentary increases in power. The pilot selected a field for an emergency landing. Due to the loss of altitude, the pilot was unable to maneuver the airplane to align the landing roll with the rows. During the landing roll, the airplane nosed over. After the aircraft was recovered from the field and transported to Caldwell, a mechanic inspected the engine. The mechanic stated that he found a small bit of black substance in the carburetor float bowl, but did not retain the substance for further inspection.