Pilot Jet Question

[Maxxed out]

Hey, I just put an HMF slip-on, and K&N Air filter w/Outerwear on my 400ex. The Pipe came with a 165 main jet, but no pilot or anything else. I put in the 165mj, but was wondering if its ok to run with the stock pilot jet? I know it doesnt seem right, but it runs fine and everything. Let me know what you guys think I should do, if I should put a Pilot jet in, what size would you reccomend? Thanks In Advance!!!!!!

[Maxxed out]

ANYONE!!!!!!!! PLEASE!!!!!!!!!!!:confused:

[cals400ex]

whats your elevation?
what is the temp your riding in?
are you running your airbox lid on or off?
any other mods done to the bike?
a 40 or 42 pilot jet will probally work just fine. some tinkering with the fuel skrew will be needed too.

by the way, a 165 keihin main will be too big if the only mods are a pipe and filter.

[cummingetit]

elevaton-5800+
temp 65+
lid off with K&N
11:1, HRC cam, e-series pipe, 155 mj (dyno jet)

I have the stock pilot in there now.
How does adjusting the fuel screw effect how it runs?

[Maxxed out]

im at 1850 ft.
temp: anywhere from 40-55 F
Airbox lid is on. HMF sent me a 165 with the pipe, and it seems to run fine with no problems even with the stock pilot jet. So should I just leave it in there? Also, should a back out the fuel screw a little?

[cals400ex]

Originally posted by cummingetit
elevaton-5800+
temp 65+
lid off with K&N
11:1, HRC cam, e-series pipe, 155 mj (dyno jet)

I have the stock pilot in there now.
How does adjusting the fuel screw effect how it runs?

that is a pretty high elevation. with you being that high, you would need to use smaller jets than what most recommend. i have never used dynojets so i can't give you a precise guess. from what i read, you would need nothing bigger than a 155, but some disagree. the fuel skrew is a fine adjustment for the pilot jet. this jet is used for the air/fuel ratio at idle. if your rich at idle, go to a smaller pilot jet if you are only one turn out on the fuel skrew. if your lean at idle, go to a larger pilot jet if you are at 3 full turns out on the fuel skrew. the fuel skrew can help determine if you have good or bad quick throttle response. however, it will not affect how your bike runs at full throttle.

[cals400ex]

Originally posted by Maxxed out
im at 1850 ft.
temp: anywhere from 40-55 F
Airbox lid is on. HMF sent me a 165 with the pipe, and it seems to run fine with no problems even with the stock pilot jet. So should I just leave it in there? Also, should a back out the fuel screw a little?


yes, the bike will run fine but you won't be getting the performance you could get. you can leave it if you prefer but there is no way i would run that jet. its personal preferance though.

for the pilot jet/fuel skrew, i would get the bike up to full temp and then let it sit and IDLE without giving it any gas for 2 minutes or so. i then check the plug. look at the color. it if seems pretty white, try turning the fuel skrew out. i doubt it will be too black with the pilot being the stock size. if i had to guess, i would probally start with the fuel skrew about 3 turns out from lightly seated. you won't have to change the pilot, but sometimes it makes the bike start easier.

[Maxxed out]

Ok, Thanks for the info!! If you were in my position, what size mj would you be running?

[cals400ex]

Originally posted by Maxxed out
Ok, Thanks for the info!! If you were in my position, what size mj would you be running?


with the airbox lid on, i would try a 155. when summer comes around i would be temped to try a 152. by the way, these are keihin jets i am talking about, not dynojets. your bike will run just fine with the 165, it probally just won't have as much power in the upper gears. going from a 165 to a 158 really helped mine out, however i had a few more mods than you so that is why i used a 158 instead of what i recommended to yourself. good luck ;)