I am planning to purchase a Dr. D pipe for my '04 YFZ450. I was wondering if I have to make any changes to my air box. I have a K&N air filter, but I haven't installed the larger adapter plate. I've noticed some people mention that they leave the air lid off of their air box. Is that recommended? I would think you would pull all kinds of dust in.

Thanks to this site I think I should be able to handle the rejetting.

Any other recommendations would be much appreciated (obviously trying to keep cost down as low as possible).

 

To get the best gains you need the lid off. BUT if you take the lid off you must rejet. If your riding around where you might get into mud or water you can either put a bunch of UNI VENTs in the lid or replace the lid with a Outwears lid cover. I have even used a old pair of pantie hose as the lid lid to keep out the big stuff. Without the lid you will also have to clean your filter more often,another reason for the vents or a outerwear cover. Your new exhaust will allow more air out so you need more air in along with more gas. Dont run without a lid unless you bump up your main jet. When do right it will make you think your own a different bike. Rejetting is not that hard. You can do a search and spend a few hours reading and know more than most of the mechanics at your local dealer.

 

Thanks for the info CamoKodiak. Accoding to the Dr. D page I will need to rejet my YFZ MAIN JET regardless. I actually just got of the phone with them and they told me that their testing was carried out with the lid left on, so that's what I'll probably do just to help protect my engine since I do a lot of dusty trail riding.

Thanks again, and have fun riding.