In recent years (since turn of the century I suppose) government has been cracking down on toxic chemicals, especially for consumer use. With EPA regulations and industrial waste control and various environmental taxes, chemical paint strippers have been dramatically neutered to the point where most of them are practically useless, and commercial chemical stripping as become prohibitively expensive. Brake cleaner, carburetor cleaner, and consumer paint stripper alike. The old standby, aircraft paint stripper, is likewise mostly non-functional these days.
But low and behold, there is now one chemical stripper that actually works, and works very well. It is QuestSpecialty Carbon-Off, available in 19-oz aerosol or pint, quart, and gallon cans.

This product is specifically marketed as "heavy duty carbon remover", and apparently it does a superb job at that specialty. I haven't tried it yet, but it should be good for removing carbon from engine cylinder head combustion chambers and pistons. The description and advertising seems to be avoiding the word "paint" (which might be an environmental duck), but the secret is too good to remain hidden. This stuff works very well as a paint remover where most everything else fails. Safe on most metal surfaces including aluminum, brass, copper, stainless steel, zinc, and pot metal cast alloy parts. It has also been used successfully on fiberglass auto body parts with no degradation, so it seems to be good for plastic composite parts as well.

- - - Corvette hood scoop bonnet. - - - Watch a 14 minute YouTube video and listen to the Snap, Crackle, Pop as the paint is peeling before your eyes in real time.