I know i couldof just serched it but i thought this would be easier.I have a 04 400ex and i just got a HMF slip on for it. I know i need to jet it but will it hurt it to run it for a little while with out the jet kit? What should i jet it to and do i need to mess with the piolet jet? IS there a aftermarket jet kit and a normal jet kit? if so what would a dyno jet kit be and what would one cost?Any help with any of my questions would be greatly appreaciated i dont know much about the subject. Thanks alot

 

Dynojet is an aftermarket kit that comes with a fuel needle and various main jets. I see them on e-bay for <$50 or go through one of the vendors supporting this website. You jet based on the mods to your engine and your elevation level. You should stick with Stage 1 unless you open up the airbox.

A 400ex carb is really easy to rejet if you have minimal skills. Here is a link to the Dynojet directions. Alternatively, you can just buy jets from the dealer and forget the fuel needle. People will argue till the cows come home about whether the Dynojet needle results in better performance.

Dynojet directions for a 400ex

 

Thanks and will it hurt it to run it with the slip on with out jetting it for awhile?

 

It could but I doubt it. Make sure you leave the airbox lid on. You don't want to risk a lean condition (too much air and not enough fuel). You aren't really going to notice much power improvement (if any) until you rejet and open that lid.

Do you know your elevation from sea level? The higher you are the richer your mixture is anyhow. What I am saying is if you are in the upper elevations you will probably have the correct jetting now anyhow.

/Jon