Hi!
35 years ago a friend of mine lay his deltawing on the pit table and when he began starting the engine it back fired with a "burp" and the fuel that had run from the silencer caught fire.
That was the first time...
The second time was during a pylonrace. One of the Quarter Midget planes caught fire during a start when the pilotbegan starting his engine (same as above,engine backfiring). The pilot tried to stop the fire which is damn hard because methanol burns nearly invisible and when the pilot sought he had stopped the flames he resumed to start the engine once more, but suddenly he felt heat comming from the engine/pipe and the the model began to burn a second time. This time the flames were put out with a fireextinguiser and the heat was canceald.