On February 25, 1995, at 1359 mountain standard time, an experimental RV-4, N872MM, was substantially damaged during a forced landing near Brighton, Colorado. The aircraft sustained substantial damage when the landing gear dug in and the aircraft nosed over. The pilot and passenger received minor injuries. No flight plan was filed for this local area personal flight which was departing Van Aire (CO12), a private airport. Visual meteorological conditions prevailed. During initial climb following takeoff the engine lost power. During the forced landing, in a freshly plowed field, the landing gear dug in and the aircraft nosed over. According to the FAA airworthiness inspector who examined the aircraft, the fuel being used was regular automotive fuel and a fuel analysis was negative for contaminates. The inspector found no evidence to indicate why the engine lost power.