Try Shell Nautilus boat cleaner.Best thing I have seen yet for exhaust smeg removal.So good infact that I bought a case lot of the stuff:)

Try starbrite black streak remover. I think I had the same problem as you. I tried EVERYTHING and nothing worked. I happened to try some Black Streak remover, and to my surprise IT WORKED. I now keep that stuff in the boat as part of my cleaning arsenal!!!!
If it doesn't work, you'll have only blown $ 6.99. . . . . .

Bill, I use the black streak remover regularly, it works great on the regular soot, This stuff is the same soot but it seems to have benn baked on and the black streak remover will not touch it.

I need to try a few of the suggestions here (boat is at my shop). I will let you know what worked. The biggest problem is the tops of the mufflers are only about 1" from the bottom of my swim platform and I can't get any elbow grease on it :rolleyes: