On August 27, 2012, about 1345 central daylight time, a Waco UPF-7 airplane, N32011, impacted terrain following a loss of engine power while in cruise near Jim Falls, Wisconsin. The private pilot, who was the sole occupant, was uninjured. The airplane sustained substantial wing damage. The airplane was registered to Minocqua Holdings Ltd. and was operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day visual flight rules (VFR) conditions prevailed for the flight, which was not operated on a VFR flight plan. The local flight originated from the Rosenbaum Field Airport, near Chippewa Falls, Wisconsin, about 1150. According to the pilot’s accident report, he visually confirmed that the fuel tanks were full before departing on the proficiency flight. The pilot observed that fuel had expanded and overflowed through the right tank vent onto the upper wing and fuselage, which was cleaned from the wing by the pilot. He had the fuel tank selector valve set on the "Both" position before to departure. After two hours of flight, the airplane had a loss of engine power. The pilot immediately applied carburetor heat, which restored engine power for about 10 seconds, and he verified that the fuel tank selector valve was set to the both position. The engine subsequently had a total loss of power where the pilot could obtain short bursts of power by rocking the pitch attitude of the aircraft up and down. The pilot selected an alfalfa field for the forced landing. The airplane’s left landing gear impacted a post and the landing gear separated from the airplane. The airplane then skidded 40 to 50 feet and slid sideways due to separated left landing gear. The airplane rolled up on its nose and right wing tip. The pilot stated, "Upon exiting I did not observe any fuel leakage from either tank cap or vent." After approximately 20 to 30 minutes, he observed that the fuel tank vents had no sign of leakage from either vent. He loosened each fuel cap and found that the left tank did not contain any fuel while the right tank did contain fuel. The pilot subsequently returned to the airplane and observed that the vent was now leaking. A Federal Aviation Administration inspector examined the wreckage. He indicated that approximately 20 gallons of fuel was reported to have been recovered from the airplane. The inspector did not find any anomalies that would have caused the loss of engine power. The pilot’s safety recommendation stated that the fuel cap should be removed and checked by blowing into the vent pipe to verify the vent is open during the preflight. At 1356, the recorded weather at the Chippewa Valley Regional Airport, near Eau Claire, Wisconsin, was: Wind 350 degrees at 8 knots; visibility 10 statute miles; sky condition clear; temperature 29 degrees C; dew point 11 degrees C; altimeter 30.09 inches of mercury.