Courtesy of various posts on the VROC List-Serv and e-mailed contributions
Vance &Hines recommends Easy Off Oven Cleaner. Spray on with pipes cold, start bike, get pipes very warm, stop bike, let cool a little then rinse off.
Gadget Note: ONLY use the spray on type cleaner. Using one of those Lye based brush on products will melt all of your aluminum and permanently scar your billet.
This oughta ruffle a few feathers, but it works like a charm... USE STEEL WOOL!!!! That's right, I said steel wool. All you do is get some warm water/dishwashing detergent solution or WD-40, soak it up in the steel wool, and have at 'er. Oh ya... use fine steel wool, and use moderate pressure. Just make sure you keep it wet and it will NOT scratch. I have been doing this for over twenty years and have never had it damage my chrome AT ALL.
Works great after long and particularly bug infested/road construction tar covered bike trips. If you're worried that it might scratch, test it on some old chrome doo-dad you have lying around or in a hidden spot. You will be pleasantly surprised. It works better than anything I have ever found for restoring any chrome to that "show room" gleam!
Use "Brakekleen" solvent, available at any auto parts store. Just make sure the pipes are cool, and DON'T get this stuff on paint, since it will remove or at least soften any painted surface. Spray the rag, then apply to pipe and rub. Don't spray directly onto bike. I continually rub my black chaps on my rear pipe and stain the pipe. Brakekleen gets it off every time.
From Ralph Lemnah: I've read many articles on removing burnt on rainsuit pants and other clothing articles from motorcycle exhaust and exhaust shields but this one works the best for me. There is no abrasive action just a good chemical removal. The product is called "OOPS" and is available at at most hardware stores or box stores. Just soak a soft cloth with the liquid and apply to the burnt on area. Repeat doing this until the area is clean.