On April 11, 1996, at 1012 Alaska daylight time, a wheel equipped Stinson ST-75 airplane, N235C, registered to and operated by the pilot, experienced a power loss and subsequent forced landing while taking off from Merrill Field, Anchorage, Alaska. The personal flight, operating under 14 CFR Part 91, was departing Merrill Field and the destination was Homer, Alaska. No flight plan was filed and visual meteorological conditions prevailed. The certificated private pilot, the sole occupant, was not injured and the airplane was substantially damaged. During a personal interview with the pilot at the accident site on April 11, 1996, he stated that he performed his runup, taxi, and takeoff on the left fuel tank. Approximately 300 feet above the departure end of runway 15, the engine lost power. He started to descend and switched the fuel selector to the right fuel tank position. The engine regained approximately 400 RPM but the pilot stated he was too low to the ground and turned his attention to landing the airplane. The airplane struck a birch tree and landed hard in the Sitka Street Park located off the departure end of Merrill Field's runway 15. The wreckage came to rest with the left wing tip resting on the ground. Examination of the airplane on site showed that fuel was leaking from the right wing tank fuel cap. The fuel was drained from the left wing tank and was found to have 15 gallons. The investigation determined that the fuel from the right tank was flowing into the left tank through the fuel valve. The fuel valve, when in the off position, stops the flow of fuel to the engine but does not stop the flow of fuel between the left and right fuel tanks. During an interview with the airplane's mechanic, he stated they had just completed installing a new fuel valve. The mechanic said he put ten gallons of fuel in the left and right fuel tanks after changing the fuel valve and they used some of the fuel to check the fuel flow. The pilot stated that he filled only the right fuel tank prior to takeoff and did not visually check the left fuel tank quantity. The pilot stated that he had a long taxi and performed a long runup. He estimated that his taxi and runup time took 15 minutes, all with the left fuel tank selected. The engine was examined and no evidence of any mechanical failure was found. The fuel line to the carburetor was disconnected and the fuel flow was checked by turning the fuel selector valve to the left tank and right tank positions. Fuel flowed freely with the selector valve in either position. The gascolator screen and carburetor screen were examined and no debris was found. The gascolator had a small amount of "fuel lube" in the bottom of the bowl. The connections to the fuel valve were compared to the schematic and were found to be correct. The carburetor was disassembled and examined and no debris was found. The carburetor was equipped with a metal float which floated when tested. According to the Stinson's Owner's Operating Manual, page 22, item number 16 of the checklist, it states the following: "turn fuel selector valve on to the tank that has the greatest quantity of fuel." The pilot selected the left tank which had the least amount of fuel, an unknown quantity less than 10 gallons.