whats best product out there to clean the carbon off exaust pipes?

The carbon (soot) collects on the limescale (do you call it that, over there?) that builds up on the upper part of the drive and particularly the tailpipes. Use a bathroom or shower cleaner with a descaling component) and it all comes off with no effort at all. Spray it on, wash it off with water. 2 minute job.
The limescale start as soon as the boat gets warmed up, and you´ll get it in salt and in fresh water, even after a short trip.

Lime Away works good on tips and outdrives.

get zep's brand of lime and scale remover...beats Lime Away hands down on my highly polished CMI tips

I use CLR that you buy at the Hardware store. Works great

CLR followed by Mother's gets them like new. They'll get bad again quickly though. It's the mineral scale that builds up.

thanks guys