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2011 kx250f WILL NOT IDLE

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Hey guys, I know I've posted about this issue before, but i have done a lot of work to try and narrow down my problem since my precious post.

 

My 2011 kx250f WILL NOT IDLE. It is driving me crazy and I have no idea why this is happening.  The bike also wont start unless the throttle is cracked open. Let me explain what i have done to troubleshoot the problem.

 

New piston and rings

New cam chain

Shimmed Valves

New Valves and valve springs

New water temp sensor

Tested TPS and was fine, but to further check, I swapped my whole throttle body including fuel injector from a precious working bike and still no difference.

Compression test came out to 60psi.

Checked air boot for leaks.

 

I feel like i have exhausted all my options... is there anything else i should try? or just have someone professional look at it and figure it out?

I would love to hear your input on my problem and if there is anyone who had this problem and fixed it PLEASE let me know.  I can also try and post a video or something if that would help you guys.

 

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Obvious but not covered, did you crank up your idle screw? 

I haven't done anything with my ECU. I figured the bike wouldnt run period with a broken ECU.

 

And as for idle screw, I have messed with it but it stiil doesnt fix the problem.  If i crank it all the way up it will idle, but in very high rpms.

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Hey guys, I know I've posted about this issue before, but i have done a lot of work to try and narrow down my problem since my precious post.

 

My 2011 kx250f WILL NOT IDLE. It is driving me crazy and I have no idea why this is happening.  The bike also wont start unless the throttle is cracked open. Let me explain what i have done to troubleshoot the problem.

 

New piston and rings

New cam chain

Shimmed Valves

New Valves and valve springs

New water temp sensor

Tested TPS and was fine, but to further check, I swapped my whole throttle body including fuel injector from a precious working bike and still no difference.

Compression test came out to 60psi.

Checked air boot for leaks.

 

I feel like i have exhausted all my options... is there anything else i should try? or just have someone professional look at it and figure it out?

I would love to hear your input on my problem and if there is anyone who had this problem and fixed it PLEASE let me know.  I can also try and post a video or something if that would help you guys.

 Just curious do you have an aftermarket pipe on the bike? 

 

  I ask because I also have a 2011 KX250F that does not like to idle. I thought it might be due to the full FMF that came on the bike. I thought maybe if I bought a power commander and played with the fueland timing I might be able to get it to idle better but don't have the money for that right now. 

 

  I did notice that on page 52 of the owners manual is says the bike should idle at 2,000 to 2,100 rpm.  

 

  Like you I can turn the idle screw up and keep it idling but in doing so when I blip the throttle it is slow to rev back down. I have not ridden it like that, but I would assume it will dramatically lower engine braking. 

 

  I am old and fat and very slow off road...lol  I want the engine braking.  But It would be so much better if it would stay idling. 

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Just curious do you have an aftermarket pipe on the bike?

I ask because I also have a 2011 KX250F that does not like to idle. I thought it might be due to the full FMF that came on the bike. I thought maybe if I bought a power commander and played with the fueland timing I might be able to get it to idle better but don't have the money for that right now.

I did notice that on page 52 of the owners manual is says the bike should idle at 2,000 to 2,100 rpm.

Like you I can turn the idle screw up and keep it idling but in doing so when I blip the throttle it is slow to rev back down. I have not ridden it like that, but I would assume it will dramatically lower engine braking.

I am old and fat and very slow off road...lol I want the engine braking. But It would be so much better if it would stay idling.

I do not have an after market pipe. It's actually funny, I returned the throttle body I bought to replace my old one and after putting my original one back on, my bike started to idle... I'm not sure how or what I did to fix it but it seems to be ok now but may need some more tweeking when I have the time. But it is definitely way better than what was originally happening

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I do not have an after market pipe. It's actually funny, I returned the throttle body I bought to replace my old one and after putting my original one back on, my bike started to idle... I'm not sure how or what I did to fix it but it seems to be ok now but may need some more tweeking when I have the time. But it is definitely way better than what was originally happening

 

I wonder if it was just a dirty TPS plug or something similar?

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I wonder if it was just a dirty TPS plug or something similar?

That's what I'm thinking. Although I diconnecterd and cleaned all the connections when I got the bike because they were filthy.

Over this past month I probably disassembled and assembled my subframe and throttle body like 5 times and for some reason this time the bike just wanted to work. I did nothing different, it just happened. It blows my mind

I wonder if it was just a dirty TPS plug or something similar?

That's what I'm thinking. Although I diconnecterd and cleaned all the connections when I got the bike because they were filthy.

Over this past month I probably disassembled and assembled my subframe and throttle body like 5 times and for some reason this time the bike just wanted to work. I did nothing different, it just happened. It blows my mind

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Well due to this thread and knowing I was going riding Sunday (today) I wound up pulling the Throttle body off of my KX.  I just wanted to look at it and see if I could see anything wrong. 

 

  First time I have had the tank and subframe off the bike. 

 

  The previous owner broke the clip on the TPS connector, and I noticed the pins on the tps were a bit corroded. I scratched off as much as i could with a file and a razor blade. I put a multimeter on it (with the bike not running) and saw that it did in fact change resistance with throttle movement. 

 

  I pulled the plunger so I could clean out the passages thinking one might be dirty. 

 

  I also pulled the backfire screen while i was there. It had crap stuck to it so rather than fight cleaning it I just junked it. 

 

  Put Dielectric grease in every connector I saw just to be safe, and thread locked most of what I touched. 

 

  On the bench It still did not want to idle. It would idle but only for 20 seconds or so. But when i went riding today tomy shock once warmed up fully and well beat on it stayed idling just fine. It's a high idle, but it does not effect the engine braking that I could tell. 

 

  Also noticed the previous owner used a CR8E plug in it, so i swapped it for the correct and odd CPR8EB-9 plug. 

 

  Now on to leaking fork seals and a valve adjustment 🙂 

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Well due to this thread and knowing I was going riding Sunday (today) I wound up pulling the Throttle body off of my KX. I just wanted to look at it and see if I could see anything wrong.

First time I have had the tank and subframe off the bike.

The previous owner broke the clip on the TPS connector, and I noticed the pins on the tps were a bit corroded. I scratched off as much as i could with a file and a razor blade. I put a multimeter on it (with the bike not running) and saw that it did in fact change resistance with throttle movement.

I pulled the plunger so I could clean out the passages thinking one might be dirty.

I also pulled the backfire screen while i was there. It had crap stuck to it so rather than fight cleaning it I just junked it.

Put Dielectric grease in every connector I saw just to be safe, and thread locked most of what I touched.

On the bench It still did not want to idle. It would idle but only for 20 seconds or so. But when i went riding today tomy shock once warmed up fully and well beat on it stayed idling just fine. It's a high idle, but it does not effect the engine braking that I could tell.

Also noticed the previous owner used a CR8E plug in it, so i swapped it for the correct and odd CPR8EB-9 plug.

Now on to leaking fork seals and a valve adjustment 🙂

That's very interesting.. Mine seems to be at a little higher rpm idle as well but it idles now compared to the 5 second idle and stall thing it was previously doing.. I can't complain. Like I said idk what I did to fix it but something worked.. I would like to dial it in to almost perfect though and I'm debating wether or not I should bring it somewhere to have it tuned up or try and mess with it myself

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That's very interesting.. Mine seems to be at a little higher rpm idle as well but it idles now compared to the 5 second idle and stall thing it was previously doing.. I can't complain. Like I said idk what I did to fix it but something worked.. I would like to dial it in to almost perfect though and I'm debating wether or not I should bring it somewhere to have it tuned up or try and mess with it myself

Yea with a full system and no backfire screen I would for sure like to get a power commander. It runs great wide open, but the off to on throttle transition is not perfect (though MUCH better than my buddies CRF450X).

 

  Did you do anything to try and clean the corrosion off the tps pins?   On the bench revving it I could tell no difference between the TPS plugged in or not which I thought was odd. I did move the TPS. I got it running and moved it back and forth while my buddie revved it and stopped where I thought it sounded the best. 

 

  I am in OKC and just use 87 octane, same as in all the bikes I have built. 

 

  I think part of my problem was that on the bench I was not letting it fully warm up before I was trying to see if it would idle. Out on the trail today it did just fine. It was hard to start a few times but that might have been me as I was super tired...lol 

 

  Super happy I bought this bike. It has been a lot of fun 🙂  

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Yea with a full system and no backfire screen I would for sure like to get a power commander. It runs great wide open, but the off to on throttle transition is not perfect (though MUCH better than my buddies CRF450X).

Did you do anything to try and clean the corrosion off the tps pins? On the bench revving it I could tell no difference between the TPS plugged in or not which I thought was odd. I did move the TPS. I got it running and moved it back and forth while my buddie revved it and stopped where I thought it sounded the best.

I am in OKC and just use 87 octane, same as in all the bikes I have built.

I think part of my problem was that on the bench I was not letting it fully warm up before I was trying to see if it would idle. Out on the trail today it did just fine. It was hard to start a few times but that might have been me as I was super tired...lol

Super happy I bought this bike. It has been a lot of fun 🙂

I actually didn't see any corrosion on my tps, but that is funny cause when I unplug mine and run it there is no different in how it runs either

Yea with a full system and no backfire screen I would for sure like to get a power commander. It runs great wide open, but the off to on throttle transition is not perfect (though MUCH better than my buddies CRF450X).

Did you do anything to try and clean the corrosion off the tps pins? On the bench revving it I could tell no difference between the TPS plugged in or not which I thought was odd. I did move the TPS. I got it running and moved it back and forth while my buddie revved it and stopped where I thought it sounded the best.

I am in OKC and just use 87 octane, same as in all the bikes I have built.

I think part of my problem was that on the bench I was not letting it fully warm up before I was trying to see if it would idle. Out on the trail today it did just fine. It was hard to start a few times but that might have been me as I was super tired...lol

Super happy I bought this bike. It has been a lot of fun 🙂

I actually didn't see any corrosion on my tps, but that is funny cause when I unplug mine and run it there is no different in how it runs either

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I actually didn't see any corrosion on my tps, but that is funny cause when I unplug mine and run it there is no different in how it runs either

I actually didn't see any corrosion on my tps, but that is funny cause when I unplug mine and run it there is no different in how it runs either

Interesting. 

 

  It may not mean anything though, as I know on the street bikes they often have a different ignition map (and rev limit) in neutral.  On the street bikes they can have a different ignition map for each gear (pretty rare) or a couple different maps that span the 6 gears (pretty common). 

 

  Be interesting to dyno the bike with it plugged in and also unplugged to see the difference. 

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Also worth note,in relation to your original post, I could never start my bike today once warm without the throttle open just a bit. 

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Hey everyone.

 

I have the exact same problem on my -11 kx250f. I also need to give a bit throttle to start the bike and there is no idle. It all started after engine rebuild. I did wash my engine and air box when my bike was in pieces. I have changed the TPS sensor to new one but I think I wasted my money on that. After reading the "Motorcycle service manual"  I think the problem might be the air intake sensor since it's failure backup is to lock the DFi in "alpha-N method" (high RPM setting). I'm gonna try cleaning the connector plug and the intake sensor pins more carefully(already put wd40 to it yesterday, hope it has affected). I'll tell you later in the evening if it worked.

Edited by Mr__Reed

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Hey everyone.

I have the exact same problem on my -11 kx250f. I also need to give a bit throttle to start the bike and there is no idle. It all started after engine rebuild and I have changed the TPS sensor to new one but I think I wasted my money on that. After reading the "Motorcycle service manual" I think the problem might be the air intake sensor since it's failure backup is to lock the DFi in "alpha-N method" (high RPM setting). I'm gonna try cleaning the connector plug and the intake sensor pins more carefully(already put wd40 to it yesterday, hope it has affected). I'll tell you later in the evening if it worked.

I would love to hear what happens, definitely keep me posted!

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The two fuel injector modes explained and the ECU backups

DFi.PNG

Backups1.PNG

Backups2.PNG

Edited by Mr__Reed

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Just got back.. Cleaning didn't work since there were no signs of tarnish in the connectors. But I'm still not giving up on this just yet because I haven't checked the sensor or wiring. Some people had changed/checked it but maybe they had a faulty connectors instead. I was thinking if someone could do a little test for us, we sure would appreciate..

 

If (hahaha) someone has a working kawi, take the seat off and unplug the connector for the intake air pressure sensor when bike is idling or start afterwords. That would demonstrate a sensor failure which should switch the injector mode to "alpha-N method" even when idling. If the bike stops idling and stalls we would know the source of this problem. If it stays running, intake air pressure failure won't affect the idle and we have one thing less to worry about.

 

I unplugged it while my bike was running and no change. Runs smooth with gas but there is no idle but ofcourse I can't know if there should be a difference because my bike is not working properly.

 

Let me know if someone is going to test this soon. Don't be afraid, it should't break anything as the pictures which I posted about the ECU backups tell, it just switches the injector method.

 

 

Edit. .... Although It may leave an error in ECU... I don't know.

Edited by Mr__Reed

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