jet kit ???

[the beaster16]

how do u install a dyno jet kit on 400ex?

[huffdaddy_400EX]

What do you mean? The kit comes with main jets, needle jets, and a few other odds and ends. Read the instruction that came with it. It will tell you what to do for your quad (where to put what and what size to use).

[the beaster16]

yea but like what size mane jet fore the ooptimal power on mx track

[tater_kamik]

that depends on what mods you have, elevation, humidity, season etc.

[bwamos]

For a 400ex with an aftermarket pipe, aftermarket filter, and a punched or no airbox lid, you want to run the stage2 setup.

Read the instructions bro.
http://www.dynojet.com/pdf/Q107.pdf

Dynojet instructions don't get any simpler.