On May 4, 2003, about 1030 eastern daylight time, a Piper PA-18-150, N9834P, was substantially damaged during a forced landing in Ava, New York. The certificated private pilot and the passenger were not injured. Visual meteorological conditions prevailed for the personal flight. No flight plan had been filed for the local flight that was conducted from a private airstrip under 14 CFR Part 91. In a written statement, the pilot reported: "...while taking off from my private airstrip...I experienced engine failure at approximately 150 feet." According to an inspector from the Federal Aviation Administration (FAA), the pilot departed to the west from the airstrip, which was on his property. The turf runway was about 2,000 feet long, and trees were located to the west, north, and south of the departure end of the runway. The takeoff was initiated, and after the airplane reached an altitude of about 150 feet above ground level (AGL), the engine lost power, started to regain power, and lost power again. The pilot reported that he was too low to attempt an engine restart, and he concentrated on maintaining airplane control. The pilot turned left toward an open field. However, he was unable to reach it due to his low altitude, and landed the airplane in the tops of trees under control. When asked, the pilot reported that he had performed his usual pre-flight examination of the airplane prior to departure. The pilot subsequently reported that he performed the run-up and takeoff on the right fuel tank. The FAA inspector also reported that the fuel selector valve had recently been replaced. The fuel was drained from the wing fuel tanks into 5-gallon cans and the new fuel shutoff valve was installed. The fuel was then poured back into the wing tanks and the shutoff valve was checked for proper operation and fuel flow. Examination of the airplane revealed contamination in the right fuel tank and the gascolator bowl. The fuel line leading to the carburetor, and the carburetor, contained trace amounts of fuel, and the fuel shutoff valve was checked and found to operate properly. The pilot did not possess a current FAA airman medical certificate, and he had not received a flight review within the preceding 24 calendar months.