On June 17, 1994, about 1330 central daylight time, a Cessna 172, N737YW, sustained substantial damage following a loss of engine power and subsequent forced landing on a field. The airplane was making a maintenance test flight when the engine lost power shortly after takeoff from Toledo Suburban Airport, Lambertville, Michigan. Neither the pilot nor the passenger (a certificated airplane mechanic) were injured. The flight operated under 14 CFR Part 91 in visual meteorological conditions without flight plan. According to the passenger/mechanic's statement, the airplane had been experiencing problems which appeared to be fuel related approximately two weeks prior to the accident. The airplane was grounded for an examination. During the examination, the mechanic found the needle valve in the carburetor was sticking. He removed the carburetor and replaced it with a recently overhauled carburetor from another airplane in order to confirm that this valve was the problem. The airplane was then taken for a maintenance test flight. The mechanic states engine operation was normal on start up, all preflight checks, and on takeoff. Approximately 150 feet MSL after takeoff, the engine lost power and the pilot made a forced landing on a field adjacent to the airport. Postaccident examination of the engine revealed a loose steel lock nut in an induction intake tube. The FAA Inspector's statement is appended.