On August 18, 1994 at 1106 Alaska daylight time, a wheel equipped Cessna 172 airplane, N78428 experienced a partial power failure during cruise flight and was forced to land at Vande Put Point, near Thomas Bay, Alaska. The personal flight, operating under 14 CFR Part 91, departed Petersburg, Alaska, and the destination was Juneau, Alaska. Visual meteorological conditions prevailed and a VFR flight plan was filed. The student pilot, the sole occupant, was not injured and the airplane was substantially damaged. According to the student pilot, he was able to keep the engine running partially by pumping the throttle. He attempted to select the left and right fuel tanks but the engine would not run. He finally selected fuel tanks "both" position and accomplished a magneto check. He stated the magnetos checked fine. He continued to pump the throttle to maintain some engine power. He executed a forced landing on the beach and during the landing roll the right wing hit a dead tree snag damaging the right wing. Examination of the airplane did not show any reason for the power loss.