On August 21, 2010, about 1145 Pacific daylight time, an experimental amateur-built Hummel/Finberg Ultra Cruiser airplane, N524DF, sustained substantial damage following a loss of engine power and subsequent forced landing near Canby, Oregon. The sport pilot, the sole occupant of the airplane, was not injured. The airplane was registered to the pilot and operated as a personal flight under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at the Mulino State Airport, Mulino, Oregon, at 1140, and was en route to Lenhardt Airpark, Hubbard, Oregon. During a telephone conversation with the National Transportation Safety Board investigator-in-charge, the pilot reported that about 10 minutes after takeoff the engine began to run rough, and lose power. He said he was unable to correct the situation and initiated an off-airport landing to a nearby field. Just before touchdown in the field, the airplane collided with a barbed wire fence and landed hard. The experimental single-seat airplane was powered by a four stoke Globe 2-cylinder horizontally opposed air cooled piston engine, rated at 35 horsepower. Postaccident examination and disassembly of the engine revealed that right and left cylinder intake valves were not properly seating with the cylinder heads when the valves were in the closed position. The pilot reported that this condition would likely cause low cylinder compression and a loss of engine power. No other anomalies were noted with the engine.