01 kx-250 rev-up on cold start

my guess is an airleak...

or ur cable is snagging somehwere?

The pilot circuit is lean. Upping the pilot one or two sizes will cure this "problem". I found the best way to cure this, if the jetting is already correct, is to start the bike with your hand on the choke, and the choke on. After the bike starts, cycle the choke on and off until it will either idle without the choke, or at a slightly fast idle. Whenever I richen the pilot to fix this problem, it ends up being too rich when the bike is warm.

Sounds like either an air leak or a tight throttle cable are your most likely suspects. Check your air boot, and also be sure you haven't routed your throttle cable incorrectly. Try turning the handlebars side to side and see if that affects the idle speed.

Darringer's reply is probably closest. While air leak's, etc normally exhibit this type of problem, some Kawi's are a little different. I've had two KDX's that both did/do it. No leaks--just "normal." As Darringer mentioned, richening jetting to cure it just made the bike rich. I either flip the choke back and forth or sit on it and slip the clutch until it calms down, then complete warmup....

Believe it or not I had the identical problem and my KX and it was caused by too big of a pilot jet! If you have the original jetting in your KX you are probably way rich. I read about the problem somewhere on this site and it was suggested to go leaner on the pilot, I just got my bike running over the weekend with one size smaller pilot jet and that problem is gone. KX's come jetted rich usually. The idle quality is also greaty improved. Either way, rich or lean let us know what you find. :thumb:

I had a 2000 KDX 200 that did that, no matter what pi,ot was in it, I checked EVERY WHERE for an air leak, natta! It was just the KDX! I'd fire it up and work the kill button for 10 seconds or so to keep the R's down until it settled down
My ATK 250, "flairs" a tad when it's cold.
The pilot jetting on both were perfect, some scoots just do it??????????????????????
Joe

My 01 has always done this, the jeting is spot on too.. Before i start it, i turn on the choke, lean the bike over til fuel comes out the vent then i slowly kick on the kick starter then i fire it.. I think they run a lil lean initially cause the carb needs fuel in the circuit..
Rick

joe28kdx said:

some scoots just do it??????????????????????
Joe

Click to expand...

Some may just do it, but they're not supposed to. Something is not quite right. Perhaps a casting flaw, or maybe a miniscule hole in the intake boot or left crank bearing that seals itself up as everything warms and expands??

I don't think it's a hole in an intake boot or a seal not sealing. The KDX did from the factory, I had the ATK rebuilt just before I got it.
Could be a flaw in the castings, but 2 bikes??, but now that I think of it, I hear a lot of scoots rev up when first fired.???????
When I was jeting the KDX I sprayed carb cleaner @ everything. If there was a leak, it'd show up. I've been a mechanic since, well before Nixon was, "The Man", and I've never had a vacuum leak that didn't change when I sprayed carb cleaner near it.
I think a 2 smoker runs a little lean when it's first fired,(fuel not "atomizing", more like droplets cuz it's a cold motor), or more likely the oil/gas left over in the crank makes it, "flair up".
The KDX I sold 3 years ago, the guy has RUN it, same piston/rings/reeds and so far it still a dependable machine, so what ever it is,it isn't hurting the motor.
I never let the KDX "race" away, thus the kill button method, (never wanted a "cold seize") .
You can do a cylinder leak down test with a SMALL amount of air, if you suspect a seal going bad, (or better yet take it to a good shop, check all your intake seals, (carb boot, gasket between the reed block and cyl. head. If they're ok, and your jetting is spot on).
As long they all check out, your oil is a good brand, your mix is spot on, and it doesn't, "red line" when you first fire it, enjoy the scoot.
Joe

Ive had 2 01 KX's(I still have 1 of em) and they both rev to the moon when started on the choke... I shut the choke off as soon as the bike is started and keep the bike running with the throttle, both bikes have done this since brand new, even after rejetting ( I ice race in the winter which requires big time jetting changes). I would chalk it up to normal starting for the bike.

crazy, my 99 kx100 also did that. I used to fear starting it in the city and sometimes it did that, I would just cringe until it went away..

Hmm, is it just me, or is this happening only on bikes with green plastic?