2007 Kawasaki kx250f only runs on choke

[Ethan Drummond]

Hello everyone,

07 Kawasaki kx250f

Its got a fmf with a powerbomb header, otherwise no other mods to the engine as far as I know. 

I have searched and performed almost everything I have seen on here but I am still having the same issue. Bought this bike a week ago. It started up with choke only and when you take the choke off it instantly dies. I have tried three different pilot jets as everyone has indicated that is the problem. I tried a #52, #40 then a #45. Bike runs about the same with any of the pilot jets in it. Cleaned the tank and put a inline fuel filter to make sure no sediments are getting into the carb. I have taken the carb apart 4 times very meticulous about cleaning every little jet and also making sure the float bowl is in spec as well. I threw a rebuild kit in and changed all the o rings and screws as well. Checked all the air intake hoses for leaks, brand new oiled air filter as well. I am hitting by head against the wall right now trying to figure out what it is! PLEASE HELP!!! BTW I am in Arizona where the elevation is about 2300ft. Bike starts easy and seems to runs fine with the choke on but obviously something is not correct for it to not idle with the choke off. 

Any input would be amazing. 

Thanks

[mlatour]

Have you cleaned/reamed the fuel passageways above the fuel screw and slow jet?  Using compressed air here may have pushed debris in even farther.

An internal air leak at the hot-start plunger's air by-pass circuit also comes to mind, excessively leaning out the fuel metering.

 

Here are some do's and don't on cleaning and servicing the Keihin FCR carburetor, perhaps some could apply to what you've done up to now:

link: https://thumpertalk.com/forums/topic/1291644-2005-yz250f-fcr-carb-maintenance/

 

 

Edited April 25, 2021 by mlatour

[steveatpa]

How many hours on it?  Hows the compression?

[Ethan Drummond]

Yes I have cleaned out the fuel passage ways every time I have taken it apart. Its possible some junk is still in there but i highly doubt it. Also I rethreaded the hot start plunger so it is in the carb pretty snug. 

I am unsure of the hours on the bike and I have not done compression test, but hearing it kick over it sounds good. 

I did just buy a new spark plug for the bike as well haven't installed it yet, could an old spark plug not let the bike idle? 

[steveatpa]

Without knowing the condition of the engine but assuming the carb is fine based on what you've already done, I'm going to guess you have an air (vacuum) leak or there's a cylinder issue, either valves or rings.  A compression test and vacuum test would help know more.

Edited April 26, 2021 by steveatpa

[Ethan Drummond]

Okay so I took the FCR carb from my 04 Honda crf250 and put it on my kawasaki. Thing started right up and ran great. So then I took the jets out of my Honda carb and put it in the Kawasaki carb. Thing started up on choke but then wouldn't idle again. Needle clip and float level are exactly the same from carb to carb. Is there an internal problem with the carb to not make it idle? I'm so lost here! 

[mlatour]

Is the fuel screw installed in the correct order :  screw-spring-washer-oring

Make sure the oring isn't doubled up (old one left in)

Did you read the link I posted earlier on common FCR wear items and specific cleaning methods?

[Slick_Nick]

Sounds like a mid-body gasket issue. Pretty common. Do a complete carb rebuild (including the mid body which is a non standare procedure) and you'll love it.

[Shawn Macdonald]

Hey guys, I know this topic is a couple years old, but I have the same issue going on here, and I got a complete new carb.  I should probably tell you I fix dirtbikes for a living, so it's not often I get stumped like this. Bike runs good on choke, kinda like it's not really on choke, but as soon as you shut choke off it won't idle, or even stay running unless you are giving it the juice.  Cleaned carb about 4x's, put everything to OEM spec, rebuilt carb top to bottom, than finally got a new carb, jetted it to OEM spec with brand new jets.  Still the same, the valves were very tight, I did reshim those, compression is good, leak down test passed, it's probably not far off from a rebuild, but it should run.  Cleaned tank and petcock, new air filter and cleaned intake boot, new spark plug, I have the hotstart cable unhooked to be sure it's returning, which bike runs with that pushed in also.  Any ideas would be helpful, I'm going to mess with this hotstart a little more, but it's brand new, don't feel like it could be leaking.

[mlatour]

Since it does the same with a different carb you can pretty much eliminate that variable but IMO,

4 minutes ago, Shawn Macdonald said:

but as soon as you shut choke off it won't idle, or even stay running unless you are giving it the juice. 

the mention of this could mean poor valve sealing despite the 'good' compression and 'passed' leakdown test.

Edited October 17, 2023 by mlatour

[Shawn Macdonald]

Yeah, that's kinda where my head has been to, I'm going to have to eat that carb and days and just go ahead and rebuild it.

[William1]

New carb? From where?

[Shawn Macdonald]

10 minutes ago, William1 said:

New carb? From where?

Ebay was all we could find, OEM wasn't available, carb appeared exactly identical besides the hot start being vertical instead of horizontal, and it came with a 135 main, 55 pilot, which I changed to the OEM sizes of 182 main 40 pilot I believe, needle 2nd position from top, air screw 2-1/4 out

[William1]

9 minutes ago, Shawn Macdonald said:

Ebay was all we could find, OEM wasn't available, carb appeared exactly identical besides the hot start being vertical instead of horizontal, and it came with a 135 main, 55 pilot, which I changed to the OEM sizes of 182 main 40 pilot I believe, needle 2nd position from top, air screw 2-1/4 out

So it is a Chinese knock off. Those are hit and miss with quality. Though they cost $200 compared to $1,000 for OEM.

What size slow air jet is in it? I'd also try a 42 or a 45 pilot (though 42 is most common for the KX250F). Also set fthe fuel screw for a base line of 1.85 turns.

New spark plug, what does it look like if you pull it out? Dork and wet? Dry?

[Shawn Macdonald]

I just took the bike out for a lap, runs beautiful and pulls hard, just won't idle, have to pep the throttle when you want to pull the clutch in and stop.

The plug I took out was a little on the dark side, but who knows how long it was in there 

[Shawn Macdonald]

This bike came in because it was leaking oil and gas, I wish I would have started it first to see how it ran, I just changed seals and rebuilt carb, than started it, it doesn't leak oil or gas, but it doesn't idle either and I have no idea if that was the case previously or if it was something I did, I can't get any feedback from the owners yet.

[Slick_Nick]

If it runs good but won't idle, what have you got the idle adjustment screw set to? These bikes it's super easy to adjust. Also what's your fuel screw set to? Post a photo of the carb installed I want to check something, both from left and right side if you can.

Edited October 18, 2023 by Slick_Nick