On July 30, 2012, about 1500 mountain daylight time, a Grumman-Schweizer G-164B agricultural airplane, N6676Q, experienced a loss of engine power near Big Springs, Nebraska. The commercial rated pilot, sole occupant, was not injured during the forced landing and the airplane was substantially damaged. The airplane was owned and operated by Downs Farm Inc. Lindsay, Montana, under the provisions of 14 Code of Federal Regulations Part 137 as an agricultural flight. Day visual meteorological conditions prevailed for the local flight, which operated without a flight plan. The pilot reported that he was climbing for cruise flight and had adjusted the engine for a cruise power setting, when the engine lost power. The pilot conducted a forced landing into a corn field and the airplane came to rest inverted. The pilot added that the fuel tanks were about three-quarters full of fuel. A Federal Aviation Administration (FAA) inspector responded to the site; the airplane sustained substantial damage to the airframe and the engine was nearly separated from the airframe by the impact. The airplane’s engine had previously been converted to another version of the engine. As a result of the conversion, the airplane had a different throttle quadrant; the engine controls were reversed from the previous propeller and mixture layout. The pilot stated that while he was adjusting the engine for cruise flight, the pilot inadvertently shut the engine off. The pilot was unable to restart the engine and elected to conduct a forced landing. The inspector noted that this was the pilot’s first spray season.