If you want to increase airflow, but not reduce water tightness, do this. Take off your snorkel, and cut about 3/4" of the intake end, then put it back on. This increases the size of the air intake from about the size of a quarter to about a two inch wide oval, and you'll still be able to go through the mud and water you could before.

Couple of other free mods:

Take off your headpipe, and look inside where they meet your exhaust port. There is a lip inside that you can grind off to improve airflow.

Modify your stock silencer (Click Here for more info on this)

These will make a noticible difference, but you will need to rejet (5 bucks or so)

 

Well, it's started...

I was at the shop on my way to Johnson Valley Friday. I picked up a Twist Throttle, And Renthal Bars to match, and Grips ofcourse. I also picked up a White Bros E Series slip-on.

Love the Sound!

Also, removed the snorkel.

 

If you're like me, and do absolutely serious desert riding(truck, buggy course, 100+miles pr. ride.), then you would probably need that ims tank, skids for everything, DG a-arm, ricochet engine ,swingarm. handguards, nerfs, bumper, shocks, steering stabilizer, out n' back rack, pipe, jets, air filter. that's only a fraction of what i'm doing to my bike, because I really take a toll on my 400ex. The twist throttle was a bad idea, it makes the bike way too hard to control.