i was just wondering how big of a difference removing the airbox lid on a 400ex is, and what changes you need to make as far as jetting goes. thank you

 

Removing the lid or air box adds power all over. Not huge but its free power. The motor makes a deeper sound with the lid off. The needle needs to be adjusted. Normaly put on 3rd position.

 

Get an EHS Racing lid, with an Outerwears cover. Flows lots of air, yet gives some protection against large stuff.

 

ive got a K&n with an outerwear, with lid off, i dropped in a dynojet jet kit, very easy to install, with just those few things and nothing else on my 400ex ive noticed great power increases as to where i can do a wheelie in 3rd gear, an di couldnt do that when it was stock, id say the stuff i described would be a great, not gonna empty your pockets improvment for the 400ex.

 

If you ride in the wet a lot, might just want to keep the lid on???????

 

Haha, yea that would be a good idea

 

I notice a 30 jet size difference between lid vs. no lid. I've been working on motors for years, while my information might be partial to my particular setup, I can tell you that the stock airbox lid is the most restrictive component in the 400ex's design, and that is a fact. The problem is that the placement of the airbox and fenders sucks, and without a lid, you're asking for trouble if you ride in the majority of conditions that ATV's are subject to. This goes for using a k&n lid as well. If you ride in snow, it will clog, if you ride in mud, hopefully it will clog as well, otherwise the airbox will fill up with water to the point that you'll feed it to your engine. Some people may say if it clogs you can just clean it after each ride, but these people do not understand that if your bike is jetted correctly to run with the no lid or the k&n lid, once it gets crud over it the bike will not run, even if you leave your snorkel attached. I'd say the only time to run the bike without a lid is during a motocross type event where the track conditions are relatively clean.
But to answer your question, you are not taking advantage of your pipe or even your k&n filter unless you ditch the stock lid. Whatever main jet you are running now, buy a couple that are 20-30 sizes larger and run the bike without the lid and you will be impressed. Then put the lid back on and the bike should blubber and die whenever you hit the throttle. That is the best way to realize this for yourself.

 

thanks for the replies people. i cant wait until spring, so i dont have to ride on the snowcovered roads. of course, we have usually have snow on the ground until may, so ive got a ways to go. right now we've got about 3 feet of snow cover, and the banks are about 6 or 7 feet.

 

I run no air box and the filter stays clean. Just use a watter repellant filter skin.

If you run no lid remove the bottom drain thing on teh bottom of the air box so if water does git in it it will drain out.