I read a tread on the difficulty of removing carbon from the combustion chamber. Now I can't find the tread again so I'll answer it in a new one. I have had great luck using berryman's B-12. You fill up the combustion chamber and let it soak a few hours and the carbon brushes off with a tooth bursh. I started using this stuff when a aircraft engine manufacture recommended using it on the turbocharge seals to remove the carbon build-up on the seals. The stuff works great. I hope this helps someone out there that was asking.