On August 15, 1999, at 1500 eastern daylight time (edt), a Brantly B-2B, N2238U, piloted by a private pilot, was destroyed during a collision with the ground during a forced landing after a total loss of engine power. Visual meteorological conditions prevailed at the time of the accident. The personal flight was operating under the provisions of 14 CFR Part 91, and was not operating on a flight plan. The pilot reported no injuries. The flight departed a restricted landing area near Jackson, Michigan, at 1400 edt. The pilot said he was flying the helicopter about 1,000 feet above the ground when the "...engine started to sputter. It sputtered until I reached about 500 feet, then the engine quit." During the auto-rotation for the forced landing the pilot said he "...flared too late and hit the tail [on the ground]." The pilot said the helicopter rolled onto its side during the ground collision sequence. The on-scene investigation revealed no mechanical anomalies that would prevent flight. Inspection of the fuel system's overboard vent line revealed it was plugged with what appeared to be mud from the Mud Dauber Wasp. The fuel system does not have a vented fuel cap. The overboard vent line is the only vent line for the fuel tank. The vent line's opening is located on the helicopter's fuselage bottom and is visible to the pilot. The helicopter's fuel vent system part's manual illustration is appended to this report.