Jetting Question

Hello, I am in the process of jetting my friends 400ex, mods are K&n filter and full WB e-series. We seemed to have the jetting close but when you let off the throttle it backfires. we installed a dynojet needle on the 3rd positon and a 155 main jet with the screw turned out 3.5 turns. any info on what i need to do to get rid of the backfiring would be greatly appriciated. Thanks

[VegasEx'r]

I think that when you are more than 2 1/2 turns out it is time to jet up (I could be wrong, though). Since you are backfiring, you are probably lean, so I would try a 160 &/or 165 jet w/ the screw @ 2-2 1/2 turns. BTW, what elevation are you at, what pilot are you running, & what slot on the needle are you using? Knowing that can help figure out the jetting.

[VegasEx'r]

Guess I should read the entire post so that I can see where the needle is :o .

Hey Snowwolfjd,

My machine runs great with the setup I have. The only difference between our machines is you have the pipe.

I am running the K&N with the modified airbox, a 165 main (dynojet), stock pilot (38 I think), and the needle on the third notch. I am planning to switch to a 160 main as I believe I am running too rich, so if you are running dynojet, I would suggest the 165 main.

[Wheelie]

Leave the 155 main jet in place, step up to a #40 or #42 pilot jet. From my experience the #40 is a bit longer than stock, this is normal. Also, set your air screw at 2- 2 1/2 turns. Good Luck!