If you want to clean the baked-on varnish from the muffler, pipe or other engine part, soak it in hot automtive antifreeze for several hours. I use a "wife donated" small crock pot. Parts are like new when they soak over night. Make sure that, if you soak any thing other than aluminum, coat it with light oil after it dries as all the protective oil will be removed and it WILL rust quickly without it.