I am working on some Stihl 31.4cc four strokes and would like to ask for some helpful hints. The engines are used and whoever used them must have used the cheapest two-stroke oil around. There is horrendous carbon build-up. I've cleaned the pistons,ports and valves easily enough. The problem arises at the top of the combustion chamber. The cylinder and the head are a one piece unit (like the Saitos). I want to get that carbon off but I don't want to damage the cylinder walls. Any brilliant ideas?

TIA

J