if you read my topic "oil spitting exhaust" you will see i had the same problem. you just need to repack the silencer.
Repacking the silencer is changing the insulation inside the muffler. Over time with a two stroke engine the muffler gets saturated with oil and cannot hold anymore. Not having anything to absorb into the oil begins to shoot out of the exhaust and land on things like the mud guard, swing arm, caliper etc.
To repack the silencer you must remove the screws or tacks from the bottom of the silencer and then pull the exhaust pipe to separate them. you will see a very black insulation in the silencer or on the inner pipe when you pull it out. This is what needs replacing.
To replace it, i just use home insulation. The pink or white insulation that goes in your walls. Just take some strips of insulation and rap them around the inner pipe and then slide it back into the silencer housing. Try to fit as much on there as you can. Don't strain yourself doing it but just try to fill it snuggly.
Good luck
here are some pictures of what it will look like and some instructions.
http://www.palmyramx.com/race_tools/2stroke_silencer_repacking.htm
