If you run the engine until it is hot the paint will "BURN" into the metal, and tend to last a little longer. I heat my cylinder in the oven to 225 degrees, and like axy said about once a year.
How much time to completely remove the exhaust?
If it takes less time then doing what I did, masking half of the bike, I'd rather do
that, plus I can paint it a lot better that way.
Multiple coats don't help?
Re: Heat.. the spray paint I got actually says it should be applied to a cold and clean
exhaust, but it just might be a precaution because it's flammable.
I actually sprayed the old scooter's exhaust when it was hot every now and then and
it was fine, but didn't last that long. Never got around to taking it completely off and
doing multiple layers though.