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2014 KX 250F idling issue

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I have a 2014 KX 250F I just changed out the valve spring and shimmed them. When starting the bike runs but doesn't idle it quickly dies. The bike only runs with the hot start on. I am new to the efi world and don't know what is wrong. Any suggestions on what to do. 

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If it ran fine previous to the valvetrain work, I'd double (triple) check the cam chain timing.

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If it ran fine previous to the valvetrain work, I'd double (triple) check the cam chain timing.
I marked the timing chain and the cam to make sure it didn't change. I also put new valve oil seals on would that make a difference?

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Curious why you replaced the exhaust springs?

 

assuming all the valves are 'shimmed' to the manual's tolerances as well.

Edited by mlatour

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In replacing the valve springs with the engine assembled,

what method did you use to prevent the valves from dropping inside while the keepers were removed?     

Compressed air, string fed thru the spark plug hole etc.

Edited by mlatour

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Curious why you replaced the exhaust springs?

 

assuming the exhaust valves are 'shimmed' to the manual's tolerances as well.

 

 

I had to replace the intake because one broke both springs and the other broke one spring broke and decided to do all of them and the seals when I had it all apart off the bike

 

 

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Okay just to make things clear, 

the top end was fully disassembled

you replaced broken valve springs (and the seals)

 

I'm not familiar with this type of failure but perhaps numerous broken valve springs would 

require deeper investigation as to why they failed in the first place before simply replacing them.

Edited by mlatour
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Okay just to make things clear, 
the top end was fully disassembled
you replaced broken valve springs (and the seals)
 
I'm not familiar with this type of failure but perhaps numerous broken valve springs would 
require deeper investigation as to why they failed in the first place before simply replacing them.
Yes the top end was fully off the bike. The valve springs were the original springs

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Quick search shows possible causes for broken springs are :

metal fatigue

installing heavier stainless steel valves and reusing the OEM springs (meant for lighter Ti valves)

overeving/valve float

spring going into coil bind due to increase lift of aftermarket cam

 

Any of that applicable?

 

When the spring broke, did the valve drop into the cylinder?

If so, that could have bent/damaged it a bit.

Edited by mlatour

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May sound overly simplistic but before getting all technical, perhaps a forgotten rag in the air box?

Seen it twice at the track this summer, engine starts and only runs on choke (not perfect but runs)

Edited by mlatour

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Quick search shows possible causes for broken springs are :
metal fatigue
installing heavier stainless steel valves and reusing the OEM springs (meant for lighter Ti valves)
overeving/valve float
spring going into coil bind due to increase lift of aftermarket cam
 
Any of that applicable?
 
When the spring broke, did the valve drop into the cylinder?
If so, that could have bent/damaged it a bit.


Like I said everything was stock before I was into it engine. I was lucky enough to hear a strange sound coming from the engine and shut it off and did no damage. And nothing in the air box. I mean the bike will run with the hot start off if you are on the throttle it has the same power when you ride it but you have to be on the gas or it will stall. And to start it you have to crack the the throttle and stay on it to keep it from stalling without the hot start

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In one post you say you took the top end completely off the bike. In the last post you've made, you said you didn't have to take the top end off. Conflicting answers. Do you mean someone else did the work? If so, I would bring it back to them if they are competent. Which at this point I would be questioning. 

If you broke a valve spring while the bike was running, It would be extremely unlikely that it didn't cause any other damage. After this scenario, at the very least would want to inspect the condition of the piston, cylinder, ports, combustion chamber, etc which would require the cylinder head to be removed. I would also be trying to find the root cause of a broken valve spring. Even with a fatigued valve train, it is rare that the spring will fail before something else went awry. 

But you did say the bike runs, just doesn't idle well. If that's the case, you didn't severely damage the engine after the broken spring.

Your best case scenario to resolve your problem, would be this >  If the cylinder head came off the bike, then you would have had to touch the throttle body where the TPS sensor is housed. If this sensor was removed or hit, it can become out of sync. It is very sensitive and even a small knock can throw it off. If we ASSUME the valve train is operable, it's properly timed, proper compression, etc, because it's running. Then I would check your fuel pump filter and checking the TPS output for .6-.62v at closed throttle. TPS calibration is very important from closed throttle to wide open throttle. It's the sensor that tells the ECU how much fuel to send to the injectors throughout the range of throttle positions. 

EFI system maintenance is often overlooked by owners. By now, your 2014 should have changed it's fuel pump's filter 4 times already!

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On 11/27/2018 at 2:03 PM, mlatour said:

Quick search shows possible causes for broken springs are :

metal fatigue

installing heavier stainless steel valves and reusing the OEM springs (meant for lighter Ti valves)

overeving/valve float

spring going into coil bind due to increase lift of aftermarket cam

Interesting. Thanks.

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I know this sounds dumb but try turning your idle up, I rebuilt my 12 and it didn’t want to run at first because the idle got turned down somehow while the throttle body was off

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