The pilot of the experimental, amateur-built airplane reported that he fueled the airplane 4 days prior to the long cross-country flight and entered 24 gallons of useable fuel into his fuel computer prior to takeoff. While enroute, the pilot switched from the main fuel tank to the wing fuel tank and the engine lost all power. The pilot switched back to the main fuel tank and the engine regained power. He had not used the wing fuel tank for some time and suspected fuel contamination in that tank; however, he forgot to reset his fuel computer from 24 gallons to 16 gallons of useable fuel to account for 8 gallons in the wing tank that would not be available. During final approach to the destination airport, at low altitude, the engine lost all power due to fuel starvation. During the forced landing, the airplane became entangled in powerlines. Examination of the airplane by a Federal Aviation Administration inspector revealed substantial damage to the left wing. The inspector did not observe any preimpact mechanical malfunctions, nor did the pilot report any. The pilot added that in retrospect, he should have done a pretakeoff runup on the wing tank as he had not used that tank in a while. Additionally, he should have made an intermediate fuel stop once he realized that he would not be able to use the fuel in his wing tank. The reason for the failure of fuel to feed from the wing tank was not determined.