2012 Kx250f idle and start problems

Idles way too high. If I try to adjust the idle down it starts to run like its normal self and then dies. Also a pain to start up now. Takes like 10- 15 mins. Just started happening like 3 days ago. Any ides?

Have you check your valve clearance?


Also turn you idle back up to where you previously had it and see if it starts easier. You may be experiencing the random high idle situation that a lot of 2012 and up kx250fs seem to be doing. Does it idle high for about 5-10 seconds and then idle back down to normal or does it do it all the time.


This should probably be moved to the kx250f section.   

Yea I brought it to two local shops and they both checked the valves and said that there was a tiny leak in the intake valve but nothing to cuase any problems but that was a good couple months ago. And yea it goes for about 5 - 10 seconds but sometimes a little longer.

It happened out of nowhere a couple days ago. The bike just started idling like it was on the choke. If I try to tune the idle down it will run normally for a few seconds and then stall. It is also very hard to start now when cold. If the bike is extremely hot it can sometimes idle on the normal speed. Any suggestions?

My guess is that the pilot circuit may be clogged

Should I buy a new one and if so what is the cost. Or how do I fix it?? And that should stop the trouble with starting as well?

Should I buy a new one and if so what is the cost. Or how do I fix it?? And that should stop the trouble with starting as well?


It's an epidemic.  I just bought a FI test light to check for any problems with the system.  Nothing.  Again, my gut tells me it has something to do with the high-idle plunger.  Again, mine is worn on visible inspection.  It was also dirty when it was disassembled.  Pressure washer, probably.  Also in my case it has nothing to do with a sticking throttle cable, or TPS, or GPS, or air pressure sensor (all checked out, calibrated, etc).  And apparently all of the FI components are good, if the light works, which it seems to.  


Symptom is the same.  Start with plunger pulled out.  Warm up.  Push plunger in.  Fine.  But when it gets hot, the idle is as if the high idle plunger is pulled out, when of course it is in.  So adjust the idle to what it normally should be.  Next time start with plunger out, fine, push it in and stall.  Sound familiar?

Sounds about like it but trying to start my bike when its cold is a pain

My bike is also backfiring alot. I think it might be valves

My bike is also backfiring alot. I think it might be valves

My bike is also backfiring alot. I think it might be valves


Could be, but if your head pipe gets super heated (it will turn cherry red quickly) the "backfire" is more likely the seal between the head pipe an head or at the mid pipe.  Just something else to look at.  An imperfect seal will also affect how it runs.

How many hours on top end?

I dont really know. I got it from someone on Craigslist. I have had it for a while now

Probably alot

Your Manuel or a parts store could tell you the spark plug for that bike. Unless you've changed it, I'd bet it's wasted. They are $5 and pull seat tank and pop the coil off and it's easy. Also put in some new gas while you have the tank off it will be easy to dump all the old gas out. Also in the back off the cylinder there is your water pump sensor 17 mm end wrench is what you use, just check.it and make sure it hasn't came loose. On the right side of the bike were the coil is there is a 8mm check that that's the ground. Check your oil breather line as well down by your linkage. Sometimes they can get clogged.

Yea I checked my spark plug already and its fine. And I was kind of wondering about the water sensor. My bike is at the shop now. But I think you may be on to something with the sensor

It was my valves

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