High revs when cold

[trevor morgan]

Hi all, I've got a 91 KDX250 which over the last 6 months with the help of this site i've made it a good all round reliable bike but there is just one thing I can't seem to solve, when the bike is started from cold, takes 2 or 3 kicks, it immediately revs up to about 1/4 throttle and won't die down to normal tick over until it's been running for 3 to 4 minutes, is this just the way they are or is there something I can try? My neighbours would really appreciate your help in this matter!!!

 

[KDXMAC]

my 98 200 does this, with choke on or off...............not sure if this is normal for all KDX's though. I don't mind it doing that lets me know when it's warmed up enough!

 

[adam728]

More than likely you are running rich on the pilot circuit and also have the airscrew set too rich. When warmed up the mixture is too rich, and therefor the idle speed screw has to be turned in to get more air in it and get it to idle. When the engine is cold it runs better off the richer A/F mixture and can use that extra air to rev up higher. As the engine warms up again the mixture is richer than ideal and rpms fall again to normal idle speed.

Next time you have your bike warmed up try setting the air screw. If you are turning it way out to get to high idle then the pilot jet is too large.

 

[trevor morgan]

I think I'm on the smallest pilot jet #38 but I will have another mess with the air screw although on my last attempt it didn't seem to make any difference to the idle speed. So what you're saying is warm it up, screw the air screw out until the revs pick up and then screw back in half a turn?

 

[Yamadad]

I was always taught that you turn the screw out until the revs change, then slowly screw it back in until the revs change, then set it at the half way mark.

 

[kdx220freak]

i have notice a rev on my kdx220 also, but it is only maybe 200 or 300 rmps higher, i was also told my jetting is rich so i would suggest maybe trying to adjust your air screw since you have the smallest pilot jet.

 

[canyncarvr]

1. A 38 is not the smallest pilot jet.

2. Hi-rev on choke-cold start is the sign of a too lean pilot...not too rich. BUT..that issue is NOT 2-300 rpm: Much higher than that.

You can 'regulate' that with the kill switch.

2-300 higher than normal idle on a choke cold start? I don't think you have a problem to start with.

The method to properly set the airscrew is under load..not by rpm. If the bike is right a quick wick of the throttle in 2nd gear at a slow walk pace should give you no hesitation..'bog' or 'boo-wah'.