On August 8, 1997, at 1115 hours Pacific daylight time, a Mooney M-20K, N321RM, collided with the ground following a loss of engine power during the takeoff initial climb from the Lakeport, Californa, airport. The aircraft was on a test flight following completion of maintenance. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft incurred substantial damage. The commercial pilot/mechanic, the sole occupant, was not injured. The flight was originating at the time of the occurrence. In a telephone interview, the pilot/mechanic stated that the aircraft was in the shop to have the left fuel tank resealed. During the procedure, all fuel was drained from the tank, and, none was put in before the test flight. After the work, the pilot/mechanic was departing on a test flight to return the aircraft to service. He stated he is positive the fuel selector was placed on the right tank, which was nearly full. Engine start, taxi, run-up, and the takeoff were normal. In the initial climb, the engine lost power and he could not return to the runway. The aircraft landed in a field and sustained substantial wing damage. He stated his belief that the fuel selector may have been leaking air into the fuel lines from the left tank. An Federal Aviation Administration airworthiness inspector from the Sacramento, California, Flight Standards District Office examined the aircraft. He reported that the left tank was completely empty and that abundant fuel was present in the right tank. The fuel line into the distributor manifold was loosened and the electric fuel pump energized; air came out of the line at first, followed by a steady stream of fuel. The line was then reconnected. Using the aircraft systems and right tank fuel, the engine was then started and ran satisfactorily. The pilot/mechanic declined to submit a written statement or complete a Safety Board Pilot/Operator Accident Report.