Won't idle when warm

[PSM]

Hello I have a 2000 gz250 with 15,364 miles that's driving me crazy lol. I've been working on my own bikes for as long as I can remember so I know a bit about fixing these things. Soon as the engine gets warm it won't idle for more then 10-15 seconds. It will idle hi or normal and then just gets slower and slower till it dies. It starts right up but the more it dies the harder it gets to restart. I've cleaned the carb a dozen times at this point and made sure the pilot jet is perfectly clean. So I know that's not the problem and I've sprayed carb cleaner all over the place will engine's running with no results so I know there's no air leaks. I've also check the petcock to make sure it's working right and it is. So what am I missing? I can't think of anything else that would cause this. Usually I clean the carb or replace a leaky hose and it fixes the problem every time know matter what bike i'm working on but this time no such luck. Any help would be greatly appreciated! Thanks!

[alantf]

Have you checked that the choke isn't stuck in the "on" position? :hmm:

[PSM]

Yes I made sure it moved freely once installed.

[PSM]

I forgot to mention that you can ride it and it's fine but when you come to a red light and it's just at idle it will die if you don't blip the throttle

[blaine]

I forgot to mention that you can ride it and it's fine but when you come to a red light and it's just at idle it will die if you don't blip the throttle
That sure sounds like something wrong in the idle circuit.It the pilot screw o-ring spring & washer in good shape?? :)

[PSM]

Just dbl checked and yes the pilot screw, spring, washer, and o-ring are it great shape. Whats the purpose of the diaphragm under the 2 screws on the side of the carb? I've never seen anything like it before. I previously had to replace the diaphragm cause the old one had a whole and it caused the idle to be all over the place so I know it adds air to something.

[Water Warrior 2]

Have you tried adjusting the idle upwards a bit? Sounds like a silly question but it may just be set too low to begin with.

[PSM]

Nothing's silly at this point but yes I've tried that. If you turn the idle up high enough it will stop the problem but then the engine is screaming like it's going a 100mph standing still lol

[alantf]

It's supposed to be 1200 to 1400 RPM with a HOT engine.

[PSM]

Not having a tach on the bike I have to set it by ear but being around bikes all my life I can tell when it's right or at least as close as it can be.

[5th_bike]

I figure your vacuum hose has no air leaks? If so, it could stop the gas from going to the carb when it idles.

[Water Warrior 2]

I figure your vacuum hose has no air leaks? If so, it could stop the gas from going to the carb when it idles.
You just had a senior moment. LOL. No air leaks should be air leaks. That would be a possibility. Also there could be a small pin hole in the diaphram of the fuel switch that only shows up at idle. Either one or both could be the problem(s).

Try running the bike in the prime position and relate the results please. There is no vacuum needed in the prime position.

[5th_bike]

Nah, I meant to say that, just maybe expressed it a bit clumsily.

Should have said "Did you make sure your vacuum hose has no air leaks?".
:)

[Water Warrior 2]

Nah, I meant to say that, just maybe expressed it a bit clumsily.

Should have said "Did you make sure your vacuum hose has no air leaks?".
:)
Heh heh, and I read it clumsily.

[PSM]

You just had a senior moment. LOL. No air leaks should be air leaks. That would be a possibility. Also there could be a small pin hole in the diaphram of the fuel switch that only shows up at idle. Either one or both could be the problem(s).

Try running the bike in the prime position and relate the results please. There is no vacuum needed in the prime position.


Yes I've tried that and it still happens. I have triple checked for all air leaks and did several test on the petcock to make sure it's working correctly. That's why this is so frustrating because all the usual culprits have been ruled out.

[Water Warrior 2]

Long shot but just maybe the vent in the gas cap is partially plugged and causing a vacuum to build up in the tank. This has been known to happen and it stops fuel flow. Release the cap after the bike quits. Try to start it again and see if there is any change.

[PSM]

Long shot but just maybe the vent in the gas cap is partially plugged and causing a vacuum to build up in the tank. This has been known to happen and it stops fuel flow. Release the cap after the bike quits. Try to start it again and see if there is any change.


Wouldn't have thought of that, thanks Ill try that today.

[PSM]

So I checked on the gas cap theory and it was a no go. Still no clue as to what's wrong. Today I even went as far as to take apart the on/off and start switch assembly and clean all the contacts but didn't help things either?

[tunil]

did you ever find the cause of your issue? im having the EXACT same issue with an 02 gz250

[Glewis950@gmail.com]

Hello I have a 2000 gz250 with 15,364 miles that's driving me crazy lol. I've been working on my own bikes for as long as I can remember so I know a bit about fixing these things. Soon as the engine gets warm it won't idle for more then 10-15 seconds. It will idle hi or normal and then just gets slower and slower till it dies. It starts right up but the more it dies the harder it gets to restart. I've cleaned the carb a dozen times at this point and made sure the pilot jet is perfectly clean. So I know that's not the problem and I've sprayed carb cleaner all over the place will engine's running with no results so I know there's no air leaks. I've also check the petcock to make sure it's working right and it is. So what am I missing? I can't think of anything else that would cause this. Usually I clean the carb or replace a leaky hose and it fixes the problem every time know matter what bike i'm working on but this time no such luck. Any help would be greatly appreciated! Thanks!



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[Glewis950@gmail.com]

did you ever find the cause of your issue? im having the EXACT same issue with an 02 gz250I have an 09 with the same idling problem if someone finds the solution and shares it with us there could be a lot of happier GZ riders [emoji4]

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[rick1987]

HELP I have the same problem very hard too set the idle either its too low or rev too much you hit the throttle and take forever to come back down .If anyone ever found what it is let us know :ride:

[Vegas Street Rider]

In many cases, it is the petcock diaphragm.

[wacio]

HELP I have the same problem very hard too set the idle either its too low or rev too much you hit the throttle and take forever to come back down .If anyone ever found what it is let us know :ride:

Sounds like plugged pilot jet.

[wacio]

Hello I have a 2000 gz250 with 15,364 miles that's driving me crazy lol. I've been working on my own bikes for as long as I can remember so I know a bit about fixing these things. Soon as the engine gets warm it won't idle for more then 10-15 seconds. It will idle hi or normal and then just gets slower and slower till it dies. It starts right up but the more it dies the harder it gets to restart. I've cleaned the carb a dozen times at this point and made sure the pilot jet is perfectly clean. So I know that's not the problem and I've sprayed carb cleaner all over the place will engine's running with no results so I know there's no air leaks. I've also check the petcock to make sure it's working right and it is. So what am I missing? I can't think of anything else that would cause this. Usually I clean the carb or replace a leaky hose and it fixes the problem every time know matter what bike i'm working on but this time no such luck. Any help would be greatly appreciated! Thanks!


Check if your petcock passages and screen are not plugged. You may have rust in tank making it into screen or even petcock. (check flow)