I got my 88" series 3 project up and running this summer. When I purchased project it had a tubular aftermarket exhaust manifold on it. I bought a new cast one like factory from our hosts here. Ive noticed its bluing like and old honda bike might. Certainly dont care about the color change...overheating is my concern as sometimes this is an indication of running too hot. Motor is a turner 8:1 with about 7k put on it from previous owner. Everything is new on it and runs great..thought ive only put about 35 miles on it this summer. Never seems overly hot after a drive, factory gauge it gets right above the white...pulled plugs they looked great. No running issues...if the bluing is normal then no worries or should I dig further?