The pilot reported that he performed a preflight inspection of his helicopter "including checking fuel tank was full and without water or other contaminants." The cross country flight was estimated to be one hour and forty-five minutes. Based upon past performance and lack of guidance from the manufacturer, he determined that the helicopter consumed about 13 gallons-per-hour, resulting in a total consumption of 22.8 gallons of fuel, which would leave approximately 6 gallons remaining in the 29-gallon fuel system. After one hour and twenty five minutes of flight time and approximately 5 nautical miles from the destination airport, the engine quit suddenly. The pilot performed an autorotation maneuver; however, the tail boom impacted a dirt and stone pile causing substantial damage to the tail boom. Post accident examination by a Federal Aviation Administration inspector revealed that "the fuel tank was empty" and a "small amount of fuel was found in both the carburetor and the gascolator." Samples from both were verified to be free of water or contaminants. A slight indication of blue fuel stain was found at the fitting for the fuel line which connects the fuel tank and the carburetor. Additional inspection and testing was performed by the helicopter’s Airframe and Powerplant maintenance technician twelve days after the accident in an effort to determine the origin of the fuel leak; however, the results were inconclusive. Fuel stains were noted on the carburetor around the split line of the two body halves, and around the fuel strainer screen on the left side.