One of the biggest problems faced by restorers of old 2-stroke motorcycles is dealing with the mufflers. There aren't many (or any) NOS replacements around for some models. The outside may be rusty and dented and the inside is coated with a tough layer of hard and oily carbon deposit from the burning 2-stroke oil in the exhaust stream. Chrome shops don't want to deal with that mess in their carefully monitored chrome tanks!
So, the first step in fixing up old mufflers is cleaning them out. If you have any engine rebuilding shops in your area, maybe you can get them to hot-tank your mufflers or run them through their jet-clean machine. Even if these methods won't remove all the carbon, they will probably remove all, or most of the oiliness. After hot tanking, if there is still some dry carbon inside, one method I've used to get it out is to put in an amount of small bolts or screws and shake the muffler around to break up the carbon. Of course. the next problem is to shake out all the screws!
Another method to remove oil and carbon is caustic soda. A web site with a good description of this method is:
http://auction.netbikes.com.au . Go there, click on the "workshop" button and then the "exhaust care" button. I hesitate to recommend caustic soda because this is some seriously nasty, dangerous stuff! Be prepared for this mixture to get VERY HOT, very fast! The caustic nature of this stuff will burn the crap out of you as well as the heat generated. Be careful or be sorry....I ain't kiddin' here folks. If the aforementioned warnings are not enough, also consider how you're going to dispose of the toxic brew left over from this process. In another post I'll describe a method to remove dents.