On April 20, 2001, about 1300 eastern daylight time, a Piper PA-31-350, N4078L, sustained minor damage while taxing at Newark-Heath Airport (VTA), Newark, Ohio. The certificated commercial pilot and passenger were not injured. Instrument meteorological conditions prevailed for the flight that originated from Fort Wayne, Indiana. An instrument flight rules flight plan was filed for the air taxi flight conducted under 14 CFR Part 135. The pilot reported that after landing, while taxing to the ramp area, a fire was observed in the left engine. The pilot secured the engine, and then he and the passenger evacuated the airplane. Witnesses extinguished the fire with a handheld fire extinguisher. Examination of the engine by a Federal Aviation Administration (FAA) inspector revealed a leak in the left engine fuel boost pump. The pump (Lear Romec model RG9080J7A) was sent to the manufacturer for further examination. Testing at the Lear Romec facility revealed that four screws, which secured the pump valve assembly, were not properly torqued. Discussion between representatives at Lear Romec and the airplane operator revealed that there was some confusion among the operator's maintenance personnel about Lear Romec Service Bulletin 101SB020 Rev. 2. According to the service bulletin, the torque of the four screws that secured the pump valve assembly should be verified, and retorqued if necessary, at certain time intervals. However, there was another set of four screws that secured the pump housing cover, in addition to the four screws that secured the valve assembly. The testing at the Lear Romec facility indicated that the wrong set of screws had been torqued. After testing the fuel boost pump and the discussion with the operator, Lear Romec issued Service Bulletin 101SB020 Rev. 3, which clarified the correct screws to torque.