I have a 2004 EFI Fatboy with Vance & Hines longshots. The joint where the pipe from the engine (which has a shield) meets the rest of the long pipe(which has no shield) is brownish for about 3-4 inches. I tried using 0000 steel wool to remove it but is won’t come off. I bought the bike like this. Would any of you know what might cause this? See the picture.

 

Heat? There's things you can take it off with but as soon as you run the bike, it'll be back...it it's heat that's causing it.

 

Check your tune.

 

Get some of this...

http://www.blue-job.co.uk/