Idunno about everyone, but the only way I really know of to toast a good ABC/AAC engine is to fly it lean. Getting it lean/hot will ruin the seal quickly. Launching an engine 500-1000 rpm down is pretty common. Sometimes this causes the engine to dribble down off of the pipe and sound very rich. But thats normal.

The use of bubble-free fuel tanks for racing saved a bunch of us quite a bit of $$ in piston/liner sets and glow plugs, since the engines didnt go super lean the last lap as the tank ran dry.