Use something Called "BLUE-JOB" you find it at your local dealer, if not at the harley dealers. Its a white powder. Anyways, My rockets had alot of bluing on them, and i used blue job to get it off. If you follow their steps it will take forever. So what i came up with is, using the car polisher, i got the pad a little wet, and then put the white powder on it, the applied it to the pipe, and turned it on,then i held it in one spot for quite some time, and all of the sudden it disappeared. Here are some pics to give you an idea of what this thing does
Notice in this picture how the bluing got to the pipe hanger (all the way from the cylinder), and then it was yellow to the end of the front fender.
BAM, these are the pipes after i used blue job on them. Notice the bluing is all gone. The pipes are mounted on my other bike in this pic, so dont think that im tricking you or something.