Correct me if I'm wrong. I'm always willing to learn.

Don't you change the heat range to a hotter plug if you are experiencing carbon fouling? The "hotter" plug has a deeper center insulator to allow the center electrode to run at a higher temperature to prevent fouling. If the fuel is combusting properly, the spark plug has nothing to do with the temperature of the engine. Plug related preignition (knocking) has to do with very hot deposits on the plug, piston or head/cyl which can ignite the fuel before the plug sparks. I have never observed preignition with our R/C gassers unless the timing was too far advanced.

Gassers do run much hotter than alkie engines. If you think your engine is running too hot then you need to rethink your cooling air flow. Proper ducting can help with over heating problems.

Ken