Why is the exhaust on my 2002 sportster blue - 2002 Harley Davidson XL 1200 S Sportster Sport

I assume you're talking about the exhaust pipes turning blue on your bike. The reason is that the chrome on your pipes has gotten heated up to the point of turning blue. This is usually caused by a lean fuel to air mixture. A lean mixure makes more power but also burns hotter. A too lean mixture destroys pistons. A richer mixture helps keep the engine and other parts cooler. Due to EPA regulatlions, Harley's come from the factory with very lean fuel to air mixtures. If your engine is carburated, you can change the jets. If your engine is fuel injected, the dealership will have to make any changes in the programming of the fuel control computer.

Good Luck
Steve