KDX Idling Problem

[trx450fm04]

I have a 1990 KDX200, my first dirtbike. It idles well on start up but after some driving, it starts to make a different idle pattern. I almost sounds like its starving for air. The carborater is clean enough to eat off of. This new idling sounds like the bike is revving up over and over. Does anyone know how to fix this?

 

[m0rie]

You might need to work with the idle and air screws after the bike is warmed up to get the idle correct.

 

[John Harris]

Primary jet is too lean since it has gotten to be warm weather. Same thing may happen if you have added a performance pipe or special reed box. Unlikely that you can cure with the air screw. I could not on my late model. Go to one size bigger on primary jet; then adjust the air screw and the idle speed. Good luck. John

 

[ridejunky]

Primary jet is too lean since it has gotten to be warm weather. Same thing may happen if you have added a performance pipe or special reed box. Unlikely that you can cure with the air screw. I could not on my late model. Go to one size bigger on primary jet; then adjust the air screw and the idle speed. Good luck. John

I am by no means a carb tuning/jetting guru but i find this contradictory.
Correct me if I am wrong but if you change nothing, wont your bike run richer in the warmer weather since there is less O2 by volume with the warmer air. If anything lean it and check for vacuum leaks

 

[John Harris]

You are correct and my memory was wrong. I had to make mine richer in cold weather. We agree the alternating race at idle is the result of a lean condition. Many things can make it lean, adding a performance pipe, air leaks as above, or even major elevation changes. Good luck John

 

[Green Hornet]

I am by no means a carb tuning/jetting guru but i find this contradictory.
Correct me if I am wrong but if you change nothing, wont your bike run richer in the warmer weather since there is less O2 by volume with the warmer air. If anything lean it and check for vacuum leaks

You are correct. Warmer temps=smaller Jet, cooler=larger jet, in most cases. Spray WD40 around the intake boot and head, listen for changes in rpm

 

[trx450fm04]

I already tried fooling with the idle screw... there is only one position where it'll stay in.. . i have to screw it in all the way and make it tight or it'll become ridiculously loose and will obvously fall out with the engine's vibrations and i know nothing about jetting... what do you mean by "one size bigger on primary jet"? does that mean buy a bigger needle??? :S

 

[jase351]

u should be able to use a medium grade of loctite which is used for high vibration i used to have a 90 model kdx done a few mods and absolutely flew but if it wasnt for loctite i would loose stuff every ride also check your engine mounts if there cracked u get more vibration

 

[Green Hornet]

If the screw is backing out from viabration, that could be why your bike will idle at the beginning and then not later