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527
Joined
10/20/2011
Location
Gothenburg
SE
My 2011 low hour crf250x have unstable idle and stalls after 30s. Then it is hard to start again but when it has cold down a bit it starts again. At higher rpm it runs and sounds good.
It seems to be a common problem on those bikes but I haven't found any answer on the root cause. It has run well for years and then after riding in mud this started. I have taken of the float bowl and cleaned all jets and float valve. I have also made sure the vent hoses are not clogged. Still no difference...
Have you cleaned the fuel tank petcock filter and the fuel cap breather tube?
No but there is a steady flow and no difference between on and reserve.
Check gas cap vent hose ?
Did it get hot ?
Coil may be bad
Yes, cap vent is ok and not running hot. It runs as normal with some throttle. After giving som gas idle is stable then after a while goes down and then suddenly stalls.
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Fuel screw set properly and installed with spring / washer/ oring ?
If you are 💯on carburetor /vents etc being clean I’d look at electrical components and connections. Measure coil and stator as per manual specifications
Check all electrical connections and clean
Try One size bigger pilot
Still not 100 that it is all clean, haven't taken apart the midbody yet. Jetting can be excluded as I have had same setting for years with no issues.
Not true, it takes just some buildup from gas sitting to plug the pilot enough to cause what you’re describing.
Try a new pilot one size larger, it’s a few dollars and a few minutes, and then can be eliminated.
I have had low and mid body of carb apart for cleaning and checked valve clearance. I also drained the tank and filled with fresh gas and still it won't idle.
The spark plug is 30-40 hours old, could it cause poor idle?
Did you put a NEW one size larger pilot jet in yet?
No, but I have tried different size jets and no change in behaviour.
Chased a similar sounding issue on my 450x. After rebuilding carb and still having the issue I spoke to someone who recommended replacing the below part. No issues since.
VALVE SET, FLOATING 16037-MEB-671$129.16 $104.62Qty:
Thanks, interesting! Could you observer wear or deterioration on the old one? I just learned from thumpertalk that you can buy the seal alone as a yamaha part. I assume the plate will not deform?
It’s been a couple years since but as I recall it did show some wear, maybe more degradation than actual wear if that makes sense.
I should add that the slide portion looked ok, I would just replace the seal.
I have purchased just the seal but you have to order from a yz250f. Way cheaper.
Thanks! Will all years of yz250f fit?
Pit Row
I believe any year from 04-13'
$20 part
All the above.... and also, take apart the hot start plunger and cable and clean and grease it well. The plunger gets corroded and gunky and starts sticking open and let's excess air in, or the air passage can get clogged closed.
Thanks, haven't thought about that!
Finally I managed to change the throttle plate seal and now it idles fine again. Though, it misfires at acceleration. Would a bad accelerator pump membrane have this symptom? I have never changed it but it looked OK.
It appeared to be the spark plug. Now it runs great!
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