Throttle haning and more!!

So I have a 2002 Yamaha YZ250F. I bought with a just rebuilt engine. So when I start the bike, which for this to happen requires the throttle screw be around 2 turns. If not it takes forever (of course). Once started the bike runs but has a hanging idle pretty high. The only way to get it down enough is with the throttle screw but then it idles well and cuts out. The best I've got the bike to run would be with the throttle screw at 2 and the pilot screw at around 2. The bike starts well, hanging idle and then when I put it in gear it idles down. But then when I give it some gas it hangs on the idle again. Do I need to do a rejet? If so I will come back with the setting I have currently.

Also, I noticed that the pipe glows which is normal. Is it also normal for the coolant to be boiling out of the overflow tube?

FYI, I will be riding at elevations from 0 to 3000 ft. Warm, humidity 50% (can get much lower), precipitation 10%

Thanks for your time. Safe riding to all.

Turn the idle speed knob down 1/16th of a turn, ride it and check, repeat if needed. You might need to open the fuel screw a 16th too.

Thanks for the info. I will try it soon once I finally get home from work.

I bought a KX250F and it had a hanging idle and if I turned the idle down even slightly it would cut out. I replaced the #42 jet w/ a #48 and now it idles very smooth and rides great. not sure how the kawi is compared to Yami but i believe they have the same FCR carb.

48 pilot is way too big for that bike. 42 is good except in death valley in the winter.

Setting the idle on some bikes is a very delicate balance of idle speed and fuel screw setting.

I am having this exact problem with my son's 2007 KX 85. Fresh filter and plug. Jetted per PC specs (which everyone seems to recommend). Idle screw and air screw adjustments seem to be way too "sensitive". The slighest turn of each and it dies. It almost seems like it is somehow vacuum or pressure related. Almost like popping a balloon if you turn the idle screw past the threshold.



When you bought the bike did it have the autodecompression conversion done to it? When you go to start it, do you need to pull the decompression lever in? It off topic a little but not that far off.

I have a 02' 250f with same prob & it was intake boot wasnt quite sealed good to carb. It was suckin air. I fixed that never a prob again. Maybe also check for cracks in intake. Hope this helps.

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