Jump to content

Recommended Posts

Finally getting this 05 KX250F up and running. It's kicking over (most times) fairly quickly. However, when it gets going it's Idling at what seems to me to be high or will die out if I start adjusting the idle adjustment. I've done the recommended jetting from 40 to 42. My question is, I know where to start the air/fuel screw but when trying to find to sweet spot for idle where do you start with the idle screw and how do you work back and forth to find a nice idle? 

TIA

Share this post


Link to post
Share on other sites

I start at 1 1/2 turns out.  Slowly turn it either way until the idle gets worse or better.  If turning it in immediately lowers the idle, then slowly turn it out until the idle starts to drop.  At that point you have found the sweet spot but turning it back to just before the idle started to drop.  I hope that makes sense.

  • Like 1

Share this post


Link to post
Share on other sites

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 fuel 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 knob 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 speed (knob) 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 fuel 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 1,850 rpm, but go by the spec in your manual.

Share this post


Link to post
Share on other sites

Hey thanks for taking the time to reply. I just realized my topic header didn't have idle screw in it. I have the air/fuel screw dialed I just want to make sure it's not a false reading because my idle screw is jacked up. So I'm trying to find the starting point for the idle screw. 

Share this post


Link to post
Share on other sites

For idle SPEED, if the carb was taken apart and you want a ball park setting for the speed, set it to hold the slide up between 1/16" and 3/32"

Fuel screw (air screw on a 2S) starting point is typically 1.75 turns from gently closed.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

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

Reply with:


×