On April 16, 2004, about 1745 eastern daylight time, N569Z, an experimental Zenith Tri-Z airplane, was substantially damaged during landing at a private airfield in Kennedy, New York. The certificated private pilot received serious injuries. Visual meteorological conditions prevailed and no flight plan was filed for the flight which originated at the Brokenstraw Airport (P15), Pittsfield, Pennsylvania. The personal flight was conducted under 14 CFR Part 91. According to the pilot, he performed a touch and go at his private airfield, and as he made a right turn in the traffic pattern, he observed fuel venting from the right wing of the airplane. He then switched the fuel tank selector position from the left tank to the right tank, to burn off fuel from that tank. He flew the downwind leg of the traffic pattern, and as he turned onto the base leg, the engine lost power. The pilot was able to restart the engine; however, it lost power again shortly after the restart. The pilot then set up for a forced landing, during which the airplane impacted trees. The pilot stated that when he switched the fuel selector from the left tank to the right tank position, he did not secure the selector into the right tank detent, effectively turning the fuel "off." He reported the accident could be attributed to "pilot error."