I have a Raptor 30 with an Ace Upgrade muffler on an OS .32SX-H which I have been running Powermaster 15% through. (Only because I had some I needed to use up!) I am about to switch to Powermaster YS 20/20 and want to clean all of the burnt on castor stains from the muffler.

What is the best way to do this?

I tried some sort of kitchen cleaner last night and it didn't move any of the stains.