When comes to the inside, my friend and I once decided to clean the muffler on his Vespa 125 1964 model. We took the muffler off and poored white spirits inside. Then we shaked it long and well, we could work in a cocktail bar after that. Poored out all the stuff in a bucket, a lot of black dirt and whatever came out of it. Then we installed it all back on the Vespa.
We started up and down the road we go, he drives and me on the back seat. After a few hundred meters he looked in the mirror and said to me; look back! I looked back. We could not see the road, due to an enormous amount of exhaust. After a while the visibility behind us cleared up a bit and we pulled aside. The Vespa was idling and the muffler was blowing out smoke rings, just as the experienced guys did who were smoking cigarettes.
We had great fun of that trip, but I can't remember if the cleaning prosess gave any significant change of performance when it comes to power. Maybe you can try and keep us updated. We did not have cell phones at that time, so pictures would be great, too!
