On April 8, 2005, about 0920 eastern daylight time, a Cessna 172P, N777UM, piloted by a student pilot and certified flight instructor (CFI), was substantially damaged during a forced landing following a loss of engine power during an attempted go-around from runway 06 (3,500 feet by 75 feet, concrete), at the Ann Arbor Municipal Airport, Ann Arbor, Michigan. The 14 CFR Part 91 training flight was operating in visual meteorological conditions without a flight plan. Neither the CFI nor student were injured. The local flight originated about 0755. The CFI stated that a go-around was executed due to excessive speed during the landing approach. He stated that upon throttle advancement, the engine lost power resulting in the forced landing. A postaccident examination of the airplane was conducted. Engine runs subsequent to the accident revealed that the engine would run rough when advanced to 1,400 rpm. A carburetor from another Cessna 172 was mounted on the accident airplane. With this carburetor, the engine was able to be advanced to 2,700 rpm and the engine operation throughout the rpm range was normal. Examination of the accident carburetor revealed that the accelerator pump nozzle tube was missing. No other discrepancies were noted.