Jetting an 09

hi all, sorry to ask yet another jetting question, i searched but couldnt find anything real conclusive.

i have an 09 kx 250f and it had the stock jetting in it when i bought it. rode it in 50 degree weather and it definately had a low end fuel starvation bog, and a hanging idle when not warmed up completely. decided to buy the FMF Jet kit to try to solve my problems but it still seems to be a little lean down low.

I live in minnesota, and ride alot during fall and spring when the temp is around 50-60 degrees, what pilot jet/main should i use and where would i buy them other than at a dealer (dealer didnt have jets for my bike)

also, could switching my needle position help with the low end bog?

What size pilot jet is in it now?

idk what the FMF jet kit gives? it was just a weird part number, didnt go by standard 40, 42, 45

the low end bog could be to rich i played with mine it runs best with stock jetting 42 pilot & adj the air screw &!!! let it warm up !

also i run a 50 leak jet. i justput in a ncyr needle i will let you know how it works on monday, its one richer than team greens nycs needle

thanks for the help guys, i better pick up a 45 and a 42, i know its a lean bog because it squirted out some antifreeze last wednesday when i was riding on the track, didnt notice it until i got back to the truck and it didnt loose much antifreeze

^ you're not going to spit out antifreeze due to the pilot circuit.. even with a 40 pilot it may bog and backfire because its lean but it wont over heat it that much unles you're letting it idle on the stand for a long time.. even rich on the pilot and idling on the stand can over heat it.

^ you're not going to spit out antifreeze due to the pilot circuit.. even with a 40 pilot it may bog and backfire because its lean but it wont over heat it that much unles you're letting it idle on the stand for a long time.. even rich on the pilot and idling on the stand can over heat it.

it must have spit out some antifreeze immediately when i stopped then.. somethings gotta be a little lean and i dont like it. it runs horrible while its warming up and never sounds like it is idling crisp. is 45 pilot a consensus?

No can really say 100% if 45 will do the trick but it's a good start....Most seem to settle at 42 or 45, I got a 42 myself and have no issues with starting and I just have to adjust the fuel screw a little bit for wherever we go.

No can really say 100% if 45 will do the trick but it's a good start....Most seem to settle at 42 or 45, I got a 42 myself and have no issues with starting and I just have to adjust the fuel screw a little bit for wherever we go.

i read up on some fuel screw adjustment, they say to turn the fuel screw all the way in, then turn it out until you reach maximum RPM and if it doesnt change switch pilot jets. noob question, why do you want to reach max rpm?

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

alright, i ordered a 45 pilot jet, hopefully fixes the prob. also, off topic, but what size helicoil kit do i need to fix the aluminum threads that fit 8 mm bolts.. im thinking 6m?

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now