What happened
The pilot was conducting pre-flight procedures when the engine began running roughly during the pre-takeoff runup. Rather than continuing with the flight, the decision was made to taxi the aircraft back for an examination of the mechanical issue. During this taxi phase, the engine experienced a significant backfire and subsequently stopped operating entirely.
Upon noticing smoke and flames emerging from around the cowling area, the pilot immediately initiated emergency shutdown procedures. The magnetos, master electrical switch, and fuel supply were all shut off to contain the situation. An FAA inspector later examined the wreckage and determined that a carburetor fire, triggered by the engine backfire, resulted in the total destruction of the aircraft.
Findings
The primary contributing factor was the engine backfire which ignited fuel vapors or components within the carburetor area. The rapid spread of fire to the cowling led to the complete loss of the airframe.