It's as much the fact that the bike is running lean as it is the fact that air is being injected into the exhaust. Hi temp exhaust gas with air mixed into it is burning off the unburnt fuel, in the exhaust header.
Some people wrap their exhaust headers with a high temp wrap, to reduce the heating and cooling of the header, hopefully, making it last longer.
I remember my old 1975 BMW discolored it's stainless exhaust, and it didn't have a bit of smog on it.
Last edited by Monterey10; 06-28-2007 at 12:07 AM.
Reason: Fix text