On August 8, 1999, at 0745 central daylight time, a Weatherly 201B, N197SK, operated and piloted by a commercial pilot, impacted a muddy field following a loss of engine power during an aerial application of a field, located approximately 3 miles west and 1-1/4 miles south of Oberlin, Kansas. Instrument meteorological conditions prevailed at the time of the accident. The 14 CFR Part 137 agricultural flight was not operating on a flight plan. The pilot sustained no injuries. The flight departed the pilot's private airport at 0700. The pilot stated that he was 100 feet agl "coming out of a 180 degree turn when the engine abruptly lost power. He was working a field from east to west. The oil and fuel pressure was "ok". The engine was barely running and he could not bring the power back up. He did not "pull" the carburetor heat during the loss of engine power. He stated that he did not have a choice of where to land as the engine stopped. During the landing, the main landing gear separated from the aircraft and its belly became shredded. Inspection of the airplane by the Federal Aviation Administration revealed that there was 28 gallons of fuel aboard. The Bendix NA-R9B carburetor fulcrum screw and the carburetor float pivot pin exhibited chatter marks. The fulcrum screw was removed after turning it 1/2 of a turn. The fulcrum screw safety wire was broken. The NA-R9B float carburetor technical overhaul manual states that the fulcrum screw is to be torqued to a value of 100-120 in-lbs.