The pilot reported that, during the initial climb, about 1,000 ft above the ground, he "saw the engine power winding down." He added that he "turned on" the boost pump, checked the magnetos and fuel mixture, and then switched the fuel selector to the other fuel tank. The engine experienced a total loss of power and then impacted the ground. The airplane sustained substantial damage to the fuselage. The Federal Aviation Administration inspector reported that he traveled to the accident, and while on-site, he observed that the fuel selector knob set screw was loose and that the knob turned freely on the shaft. The set screw doesn’t keep the knob keyed; it just stops it from coming off. A roll pin keeps the shaft in position and was observed in the selector well. The pilot did not submit the National Transportation Safety Board Form 6120.1 Pilot/Operator Aircraft Accident/Incident Report.