On July 3, 1996, at 2115 central daylight time, an experimental Hewitt Cassutt 3M, N290E, sustained substantial damage when it landed hard during a forced landing due to loss of engine power. The private pilot received minor injuries. The 14 CFR 91 flight departed Vermillion, South Dakota, on a local flight. Visual meteorological conditions prevailed and no flight plan was filed. The pilot reported that the engine had been running rough at higher altitudes at low power settings. He reported that he had made some adjustments to the engine and flew the airplane to test the engine. He climbed to 8,000 feet and he reported that the engine operated normally with no indications of a problem. He returned to the airport and did one touch and go. He reported that he landed hard and bounced the airplane. He applied full throttle and did a go around. At about 500 feet the engine quit. He made an emergency landing in a bean field one half mile south of the runway. The pilot reported that the engine used on the experimental aircraft was a Lycoming O-290-G, which was originally used as a ground power unit. The fuel pump on the engine was the original fuel pump and had not been certified for flight. Examination of the engine by a Federal Aviation Administration inspector revealed that the ignition system operated. The pilot reported that he had fueled the airplane with 12 gallons of fuel prior to flight and he never flew it with less than one half tank of fuel. The pilot reported that the fuel pump had a vacuum leak. He reported that the valve would not seat enough to create the necessary suction.