Just wondering what others have done to their 400 EX's to make them even faster. I have the FMF Power-Core IV-2 pipe and K&N jets and filter ordered. Other than that, I'm completely stock. I'm wondering what else I can do to increase performance and get all I can out of my machine. Do I replace gaskets, sprockets, etc? Any info would be much appreciated. Thanks guys.

 

You could also buy the new FMF Powerbomb head pipe...supposedly it increases flow by 10% but without raising the noise level...kinda expensive though. You could also install vent plugs in the airbox cover, or run without a cover at all. As far as extracting maximum performance out of the engine though, it all depends on how much $$$ you have to spend. BTW, be sure to post your results after installing the new IV-2 pipe...that's the one I'm looking to buy also.

 

Check to make sure your getting full throttle ? I would like to know how your bike runs with the FMF Power core IV-2 also.

 

New sprokets, a cam, a big bore kit, high compression piston, new valve springs (must have with cam), etc etc
There is tons of stuff to do to the 400EX to make it faster and more powerfull. Sounds like you got a good start, the next thing I would get is a cam, get a White Bros fast track cam and you wont be sorry.

 

I would suggest a Web Cam 450/451 grind with hardened rockers. The stock springs work with this cam.

 

I would suggest a Web Cam 450/451 grind with hardened rockers. The stock springs work with this cam.

 

I added a White brothers cdi box on mine and now I can make it up the face down to big sand mt. I'm still lacking in the top end. Look down to the dunes, there is usually some 400's with a 430 kit in them. They do the trick but why tear in to it yet? You can get a better deal on parts down to Monarc in orem for parts. I got my cdi for 99.00 down there. I know quadfever has one there too for 125.00. Let me know if you ever need someone to go riding with, anytime.

 

I'm pretty impressed with the 400EX the way it is. The only performance that I'm interested in is: out of the hole, so I've ordered a 14 tooth front sprocket to replace the stock 15 tooth.

 

Azrob,
Where did you order your 14-tooth sprocket from? What was the price? Please post your results (acceleration, enough engine power, etc.) after you put it on.

 

WHITE BROS, JAMES LUCKY, and NAC'S RACING do sell different sprockets. SIDEWINDER also make a lot.