On February 26, 1994, at 1435 eastern standard time, a Helio HE391B, N9050R, nosed over during an emergency landing to a private airstrip near Saluda, South Carolina. The ferry flight operated under 14 CFR Part 91 with no flight plan activated. Visual weather conditions prevailed at the time of the accident. The airplane sustained substantial damage; the pilot was not injured. The flight departed North Myrtle Beach, South Carolina, at 1245 hours. According to the pilot, he worked several weeks on N9040R, and completed extensive maintenance on the airplane. The repairs included the installation of a rebuilt engine and the installation of two remanufactured fuel tanks. During the installation of the fuel tanks, serviceable fuel caps were not replaced by the pilot and mechanic as part of the fuel tank installation. Since the aircraft maintenance logs were lost, and the airplane had not flown for several years, the pilot requested and was granted a Special Flight Permit from the Federal Aviation Administration. Under this provision, no annual aircraft maintenance inspection was required to conduct this flight. While enroute to Abbeville, South Carolina, at 4000 feet mean sea level, N9050R lost engine power, and the pilot's efforts to restart the engine failed. The pilot located an airstrip, and executed an emergency landing; the airplane touched down on the south runway at a 45 degree angle and flipped inverted. During the on site examination of the airplane, fuel was observed leaking from the left fuel cap. The pilot stated that the normal fuel endurance for the airplane is four hours; the airplane was full of fuel at the last departure (see attached pilot/owner accident report). The subsequent examination of the airplane revealed that the left fuel cap leaked fuel, and there was extensive wear on the fuel cap locking lugs. According to two operators of the Helio 391B type aircraft, they have experienced the same type of engine malfunction resulting from worn fuel caps. Both operators believed that a loose fuel cap in-flight prevents the gravity flow of fuel to the hopper tank, which results in the loss of engine power (see attached FAA personnel statements).