jetting this set up 400ex

[supernatural]

I know there are tons of jetting posts on here but i needed to ask this. i ordered an hmf slipon and jet kit and know their recomendations. i also got a open airbox system from ehsracing.com (check it out pretty slick) which is supposed to to be like runing no airbox lid. question is will the jetting change or should i stick with hmfs 152 kehein and 42 pilot or what do you think?

[EricCartman]

I have an almost similar setup. If you are gonna change the airbox lid - I am HOPING you're gonna get an aftermarket filter. If you don't - you're gonna be choking the engine and the lid is gonna be almost useless.

If you're riding dusty stuff, get a UNI.
If you are muddy or wet, or similar with not much dust, get a K&N.

A pipe is a pipe as far as jetting is concerned.

I am running the Keihin 155 main jet.
Using a Keihin 42 pilot jet.
Took a needle washer and put it under the stock 3rd clip position. Basically gives it a 2.5 clip position.

I checked my jetting with the spark plug - it's very close to dead on.

Don't waste the money on the jet kit - just change the parts as I did.

[cals400ex]

a lot of it will depend on the brand of jet kit you bought. for example, a keihin 152 is NOT the same as a dynojet 152. plus, the needle plays a role in which mainjet you might need. if you use a stock needle and keihin mainjets then i would start around a 160 with the air box lid removed/EHS lid.