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.
- two 1/2 inch rubber vacuum caps
- one 3/16 inch rubber vacuum caps
- one 5/8 inch rubber vacuum cap
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):
Remove seat (8mm). Remove speedometer housing (8mm), don’t forget the cable and wire bundles. Remove fuel and vacuum lines from petcock. Be sure to put a few rags under this, as some fuel will leak out. Now take the front and rear fuel tank bolts (12mm) out and remove the tank. If you have a tire laying around, it makes a nice place to set the tank, otherwise place it on a few old towels.
Locate the hoses between the valve covers… they looks like a T and go to a gold air valve. Take them off of the valve covers, and place the 1/2 inch vacuum caps over the ports on the heads. Now, remove the small hose from the gold air valve runs to the T fitting connected to the petcock vacuum line, and plug it with a 3/16 vacuum cap. Lastly, remove the large hose that goes from the gold air valve to the back of the air cleaner assembly. Put a 5/8 inch vacuum cap on the back of the air cleaner assembly.
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.