What happened
The aircraft experienced an engine fire while attempting to start the right engine on the ground. The pilot reported that the engine failed to start during the initial attempt. During a second attempt, the engine successfully started but was running on primer fuel when the pilot heard a loud bang and observed flames coming from the engine compartment.
The pilot attempted to run the engine to draw the flames into the intake in an effort to extinguish the fire, but this method failed. The pilot then secured the aircraft and evacuated. Airport fire department personnel arrived and completely extinguished the remaining fire.
The investigation
Post-accident examination of the right engine revealed that the carburetor float assembly was cracked. This structural failure allowed the float to sink, disrupting normal fuel level regulation within the carburetor. When the fuel boost pump was engaged for the starting procedure, fuel flowed unchecked through the carburetor and out into the intake scoop area.
This excess fuel spilled onto the aircraft structure and the ground below. The loud bang heard by the pilot was identified as an engine backfire, which subsequently ignited the accumulated fuel spill, causing the fire observed during the start sequence.