Carbon build up in a motor that's had like 2 gallons on it? Comparred to a 1/1 car with, say, 50,000 miles on it?
I can see a real car building up carbon, they all do it. They drive thousands of miles and most people don't get on them hard enough frequently.

An RC engine is not a 1/1 engine and it's not driven the same way. I've seen Revo2K drive, he gives it all it has and then some.

My initial thought when I saw the pic was he ran rich for awhile, had lube build up, then ran it hot making the lube burn.

What makes burned black substance anyway? a cold, rich engine? The only way to burn things is give them too much heat.