This procedure removes the fresh air system that dumps outside air into the exhaust system just after the exhaust valves in the heads. It will lower your exhaust temps (control the blueing of your pipes!) and kill a lot of the backfiring during gear changes and decelleration.
You should be able to get all the parts listed at an auto parts store, like Pep Boys, Autozone, Napa, etc.
Procedure (for non- Ca. models):
Here's a picture of one of the plugs that I used to block the air inlet on the head of the rear cylinder, as seen from the left side of the engine
That's it...you're done! Some people have mentioned that they could plug the large lines connecting to the front and rear cylinder heads without pulling the tank and seat, so take a flashlight and have a look at your bike and see if you're one of the lucky ones. If so, shove a marble in each of the large hoses on the cylinder heads and leave the rest alone!
One last alternative, offered up by Scotty on VROC, is to install a piece of hose between the two ports, blocking the input of outside air. This works great, and is a good alternative to the rubber vacuum plugs I mentioned above.