eraser, I have never had any reason to believe that this was an issue. I use the johnson mufflers and they are very close to the carb. One thing I have improved over the years is the baffling to force the incoming air through the fins. This is very low-cost and can't hurt anything. For the first couple of years I did not use any baffling. I have seen others do the same. But it gets hot here in st louis and I think the baffling helps out a little.

Another thing to check: every year or two I have to remove the cans from the engine and "de-carbon" the insides of the combustion chamber. This is a relatively easy repair and can make a world of difference in all around running if you have a lot of hours on the engine. Once the rings had so much carbon on them that they were effectively stuck in the grooves. Each cylinder comes off with just four bolts. You can leave the engine on the plane (remove the cowl), and pull the cans off. Clean the inside real good (I use a paint remover) and if the rings are stuck on the pistons, remove them and clean them. The cans slip back over the pistons and rings quite easily. You just compress the rings with your fingers as you guide the cans back on to the piston. The bottom of the cans are bevelled to help slip these back on. I put in new spark plugs at this time also.

I'm not sure why this carbon develops, but some will say too rich running, too much oil or too hot running. perhaps it is normal to some degree for a 2C engine.