Air Filter? Rejetting ?

[400exRider123]

Would i have to rejet after putting a k&n flter on my 400, if so what shouls the jet size's be

[underpowered]

yes you need to re-jet. try going up one on the main and you may need to adjust your needle

[400exRider123]

What would the size be so i could get one, and is it a must becasue i heard that you didnt have to :confused:

[underpowered]

if it has a stock jet in it now, you need a 145 Main. IT is not an absolute must, but very highly suggested. you are giving it muchmore air so you have to add fuel to accomadate for this. other wise it will run lean, and lean is very bad.

[04'400ex'er]

Originally posted by underpowered
if it has a stock jet in it now, you need a 145 Main. IT is not an absolute must, but very highly suggested. you are giving it muchmore air so you have to add fuel to accomadate for this. other wise it will run lean, and lean is very bad. Stock main jet on a 400ex is a 148,and the Pilot is a 38 if im not mistaken. If you add a K&N filter, remove the airbox lid, and remove the exhaust baffle, a 152 main will be just right. If I were you I would go ahead and try adding a 42 pilot also. It might be a little rich, but more than likely you will be ok and will also help your bike start alot easier. The clip on the needle should be fine though...

[400exRider123]

thanks
but i need the baffle people in my nieghbourhod complained to much when i had it out