It is fairly common for ill-tuned engines to do a "lean spit" through the carburetor, especially during shut-down. Eventually you sort of automatically watch for it. The ancient Kirby-Lauson engine'd rotary I had about a thousand years ago set fire to its air cleaner when I shut it down one day. I was very, very tempted to let it burn, but I finally put it out - though I've never been sure it was a good idea.
Long ago when cars had carburetors and some slackers or hoons left off the air cleaners, it was not terribly uncommon to see cars with burned areas on the bonnet directly above the carburetor.
