Buddy of mine called me this morning to ask me what was wrong with his 15.5 HP Briggs OHV on his grass cutter. (i know this ain't a place for grass cutter questions, thats why its in the coffee shop... ) he said the shroud (this is a 05 model, so its a plastic shroud) caught on fire right before he shut the mower down after cutting all his grass. what in the world could cause this? I had to adjust the valves a few weeks ago when he got this mower (bolens) , but you have to pour a little gas in to start it (carb needs rebuilt or cleaned, then it fired right up, ran fine, we changed the oil in it after it warmed up.Thats all thats been done to it, and it didn't have a air filter so we made a temporary one out of foam rubber because i didn't have one, i ordered one for him. I haven't seen the engine so i can't tell you where the fire started. My guess is maybe he poured a little to much gas in and got the filter wet then motor backfired through the carburetor and caught it on fire? you would think the gas would evaporate after all that time. first time i've ever heard of a lawn mower engine caching on fire!!!!!!!! What else could cause a motor to catch on fire like this? thanks guys!