The experimental amateur-built airplane had not been operated for several years before the pilot purchased it and attempted to return it to a flight-ready condition. The pilot completed two test flights and then completed a circuit in the airport traffic pattern during the third flight. After approaching the runway and flying down its length to assess the airplane’s handling characteristics in ground effect, he attempted to add power with about 500 feet of runway remaining. At that point he realized that he was unable to move the carburetor heat control in order to deactivate it, and lacking sufficient runway to land, he decided to fly the airplane around the traffic pattern about 200 ft above ground level. While maneuvering back to the runway, the engine began to lose power and the airplane’s sink rate increased. The pilot leaned the mixture and changed fuel tanks; however, he could not restore engine power. He then performed a forced landing to a marshy area, during which the airplane sustained substantial damage to the fuselage and wings. The wreckage was not recovered from the accident site and could not be examined, therefore a reason for the partial loss of engine power that the pilot reported could not be determined.