According to the pilot, 10 minutes into his flight back to home base, the engine backfired and stopped running. Terrain for an emergency landing was unsuitable, but he went for what he considered the best option, and collided with a farm tractor. The collision separated the aircraft's propeller and nose landing gear. Postcrash examination of the airframe and engine by FAA personnel revealed adequate, uncontaminated fuel aboard and a cracked carburetor body at the main fuel feed line attachment that appeared to have existed precrash.