Sinclair International has the best carbon remover I have ever used. It is called T&M. I use Sweets 7.62 to remove heavy copper fouling followed by T&M to remove the carbon. If lightly fouled with copper I just use the T&M as it also removes copper. If anyone can put their hands on a ancient can of benzine noting beats that. When I was a kid I use to dip motor cycle spark plugs in it and they would look like brand new plugs after dipping. I had a small can of it and it removed all carbon soft and hard with three patches. Sad to say it ran out.
Best regards,
Grit