don't know what type of coat you want, but if you want a cheap and durable black finish, pick up some rust stop spray, all kinds of brands out there normally a phosphoric acid blend, clean up the pipes getting all the loose rust off and wash with soap and water to get all the oil off too, then spray the pipes real well with the rust stop let it dry and run the bike a while to heat cure it.
it ends up looking like a set of new black pipes, lasts a long time, the pipes on my bike were done early last year and look great still, I have a set sitting in a pile of other junk behind the garage that have been there for a few years (damaged, but someday I may need a part from them) and they still look great.
running them too hot (as in bad tune) will turn them greyish right on the top of the bend at the head, but tune up and respray th area and they look good again.
Ken.
