On September 15, 2002, at 0815 central daylight time, an Ercoupe 415-CD, N3989H, sustained substantial damage when it had a partial loss of engine power after takeoff and nosed over during a forced landing to a cornfield. The commercial pilot and the passenger were not injured. The 14 CFR Part 91 positioning flight was departing from runway 29 (5,100 feet by 75 feet) at the Effingham County Memorial Airport (1H2), Effingham, Illinois. The final destination was Santa Monica, California. Visual meteorological conditions prevailed and no flight plan was filed. The airplane was purchased on September 13, 2002. The airplane received an annual maintenance inspection on September 13, 2002, prior to the sale of the airplane. The pilot reported that he and the new owner picked the airplane up at Chapin Field (1B8), Cambridge, New York, and intended to fly the airplane to Santa Monica, California. They departed 1B8 and flew to Ithica (ITH), New York, on the first day of the flight. They flew to 1H2 on their second day of the flight. The pilot reported the flights were uneventful. The pilot reported the following information concerning the accident flight: "Fueling, preflight, including gas sampling, were normal. Engine start & taxi were normal, however while back taxiing on runway 29, I pulled the Carb. Heat & the engine noticeably ran better. Mag check and run up were normal, minimal differential when carb. heat checked...On take off carb. heat was placed on. The ground run was acceptable & a positive rate of climb was established. At 300 feet +/-, I pushed in the Carb. heat. With no change in engine sound the aircraft began to sink soon after. Prior to touchdown I pulled the power off to minimize engine damage. Landing in a cornfield a few hundred yards from the runway followed...Touch down was on the main landing gear followed by a nose over as the nose wheel dug into the soft dirt." A Federal Aviation Administration Airworthiness Inspector conducted a post-accident examination of the airplane. He reported that an engine exhaust valve was stuck open.