On January 31, 2000, about 1627 eastern standard time, a Beech D50E, N14VU, registered to a private individual, experienced a fire at the left wing while taxiing to takeoff at Myrtle Beach International Airport, Myrtle Beach, South Carolina. Visual meteorological conditions prevailed at the time and an instrument flight rules flight plan was filed for the 14 CFR Part 91 personal flight. The airplane was substantially damaged and the airline transport-rated pilot, the sole occupant, was not injured. The flight was originating at the time of the accident. The pilot stated that after landing following a 4.8 hour block time flight, all four fuel tanks were filled. He performed a preflight to the airplane and started both engines with no discrepancies noted. While taxiing to takeoff he performed a flight control check of the ailerons and while looking at the left aileron, he noted discoloration of the paint on the upper wing surface outboard of the engine nacelle. He requested fire rescue assistance from the ground controller and taxied to an open area of the ramp, where he secured the airplane. After exiting the airplane he noted fire at the outboard fuel tank vent which was leaking fuel. He discharged a hand held fire extinguisher he obtained from the airplane and nearly extinguished the fire. The airport fire rescue then responded and extinguished the fire using only water. According to the airport fire department incident report, vented fuel ignited by exhaust manifold was cited as the "preliminary cause" of the fire.