To make your 400 faster it would help to get more power and you can do that just by getting an aftermarket airbox.I did this to my quad and it gave me a pretty good boost in power.

 

well he has a K&N filter so I asume he has the airbox lid off or cut holes in it and rejeted his carb. Am I correct guy? If not then do that it will make you faster.
Try a 155 main jet,with a 42 pilot jet,and lower the clip on the needle jet one notch
Either take your airbox lid off completly or cut some good sized holes in it.
Ignore this post if you have already done all this.

 

yeah we know the dangers but we with the airbox lids off don't ride in water.

 

I'm from Pennsylvania there is a lot of mud here and we need a lid so we dont flood and LTearnhardt is from Tennessee so i would think that there is some mud down there and if he takes off his lid he would probably take in a lot of water if he rides woods.

 

ur right joe, i need my airbox lid its muddy where i mostly ride

 

LTearnhardt@hotmail.com

 

You can still stay safe and be cheap if you get the 1 inch uni filtered airbox vents for 7 buck's you get six of them. then you drill 6 one inch holes in the airbox and snap the vents in, no mud will get in.. it would be best to get an outerwears cover for your k&n filter too.
just tryin to save you money, this is how most people do it anyway.
try EXriders.com and search for airbox