On August 30, at 2218 Alaska daylight time, a wheel equipped Stinson 108-1 airplane, N9130K, registered to and operated by the pilot, experienced a power failure during cruise flight and was forced to land in the trees approximately 14 miles southeast of Anchorage, Alaska. The personal flight, operating under 14 CFR Part 91, departed Seldovia, Alaska, and the destination was Merrill Field in Anchorage. A VFR flight plan was filed and visual meteorological conditions prevailed. The Private Certificated Pilot and his passenger were not injured and the airplane was substantially damaged. According to the pilot, there was no warning and no backfire and the fuel tank from which he was operating indicated 3/4 of a tank. The airplane was inspected after it was recovered and no fuel was located in any of the fuel tanks. However, the airplane remained upside down in the trees for a few days before it was recovered. The fuel selector valve was examined and it was found to bind during rotation between all of the positions. There were no indentations at any of the positions. The available positions were "RIGHT, LEFT, and OFF." The fuel selector valve was marked with the correct positions listed but the placard was not from the original manufacturer. No other mechanical abnormalities were found with the airplane.