On July 19, 2005, about 1030 eastern daylight time, a Piper PA-22, N2645A, piloted by a private pilot, sustained damage when the airplane nosed over during a forced landing following a loss of engine power on downwind to the Plainwell Municipal Airport (61D), near Plainwell, Michigan. The personal flight was operating under 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file. The pilot reported that he had sustained minor injuries and that his pilot rated passenger was uninjured. The local flight originated from 61D at 1025. The pilot's accident report stated: [The passenger] and I had installed the overhauled carburetor on July 18th and ran up the engine to verify proper working condition. ... On the 19th we ran it up twice to double check - everything was operating properly. The 11:25 am take-off was smooth and the climb out was strong. We turned crosswind, then downwind [1,000 feet above ground level]. On the tailend of the downwind, I pulled the carburetor heat, then pulled more power back. Five seconds later, I went to put more power in but the engine was dead. [The passenger] took over as pilot in order for me to troubleshoot (working with the fuel selector, carburetor heat, throttle and mixture). We immediately turn toward the airport. Our descent rate exceeded our distance to the airport, so we headed for the closest field. It appeared to be a bean field, which would have been hard packed and flat. However, it was a potato field, which was soft, soaked from recent rain, and uniform with 1 1/2 to 2 foot deep ruts. The landing was fine until the nose gear hit and dug in. The plane flipped over onto its top and slid to a stop. A Federal Aviation Administration Inspector examined the wreckage. No pre-impact anomalies were detected with the airframe, engine, or carburetor. At 1153, the recorded weather at the Kalamazoo/Battle Creek International Airport, near Kalamazoo, Michigan, was: Wind 240 degrees at 9 knots; visibility 10 statute miles; sky condition scattered 4,700 feet; temperature 28 degrees C; dew point 16 degrees C; altimeter 30.05 inches of mercury. A copy of a Transport Canada Carburetor Icing chart was reviewed. The temperature and dew point were plotted on the chart and their intersection falls in the serious icing - descent power area of the chart. The icing chart is appended to the docket material associated with this case.