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kx250f won't start

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hello,

this is a 2006, I bought it from a guy that broke it while driving it with no oil. it overheated. its still in good shape almost not used

I redid the top end. piston and rings was scrapped. cylinder has no damage. I have a compression of 45 psi , it should be between 62-102.

I also changed the coil because it was shocking me when i was testing the spark plug.heat may have damaged it. now I have good spark

I have plenty of fuel coming to the chamber because the spark plug is wet

I measured the valve clearance exhaust is okay still at oem specs both at 0.22mm, but the intake one is out of specs of 0.01 (0.09 should be between 0.10-0.15)

may be I should play with the fuel ratio with the idle and fuel screw. even though I have it at 2 1/2 turns

 

I dont know why it doesnt start. What would overheating break?

I tested the magneto I have a good voltage and resistance

im fixing it at 5 celsius its getting cold everyday

 

any ideas?

Edited by Maxi123

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Pilot jet im pretty sure is oem

I just ordered some shim 

I will tighten the fuel screw next time

Edited by Maxi123

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I thought it was air coming from the air filter but it was oil leaking from the breather tube when cranking.it was doing a bubbling garbish sound it was filled at middle of the viewing glass though. I lost some oil while cranking.

 

Yes compression is a little low  i am trying to figure out where air is leaking. I will start with shimming the intake.

Edited by Maxi123

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Yes, It was the intake cam that was holding the valve open.I shimed it and It started and I let it warm for few minutes while adjusting the speed and fuel

Thanks for help

Im surprised it only take 0.02mm out of specs for not working

Edited by Maxi123

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The no start problem is 9:10 the intake valves clearance getting too tight.
With respect to compression test, you will not get an accurate reading because the exhaust cam has an auto-decompression device on it. That releases pressures at kick over speed. To get full compression reading disable the device first by removing it from the cam.

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4 hours ago, FaceDeAce said:

The no start problem is 9:10 the intake valves clearance getting too tight.
With respect to compression test, you will not get an accurate reading because the exhaust cam has an auto-decompression device on it. That releases pressures at kick over speed. To get full compression reading disable the device first by removing it from the cam.

Youre right, when i measured it after shimming it was the same pression as before. Now it is running good . I'm happy i could fix this bike

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On 10/20/2018 at 4:56 AM, Maxi123 said:

Im surprised it only take 0.02mm out of specs for not working

Maybe the valve clearance was tighter than you measured.

I find that because I must bend the feelers so much to get them under the intake cam lobes that it's not always easy to feel when it's a free slide into a gap or if it's pushing the bucket down a little.

19 hours ago, Maxi123 said:

I'm happy i could fix this bike

Assuming you have Ti valves, then re-shimming clearance is a temporary fix. Once the plating on the rim of the valve is worn through, then the soft Ti will erode away.  If you keep the RPMs down then I found the worn valve lasts a lot longer.  Recently I adjusted a tight intake valve back to 0.15, and it worked well for 2 ride days (4 hrs) going easy on the motor.  Clearance measured the same. Then on the 3rd day I went hard on the motor and revs, and the valve pull up to zero clearance after about 15 minutes. Now it has two new OEM Ti intake valves installed and runs great.  Head seats looked excellent.

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3 hours ago, numroe said:

Maybe the valve clearance was tighter than you measured.

I find that because I must bend the feelers so much to get them under the intake cam lobes that it's not always easy to feel when it's a free slide into a gap or if it's pushing the bucket down a little.

Assuming you have Ti valves, then re-shimming clearance is a temporary fix. Once the plating on the rim of the valve is worn through, then the soft Ti will erode away.  If you keep the RPMs down then I found the worn valve lasts a lot longer.  Recently I adjusted a tight intake valve back to 0.15, and it worked well for 2 ride days (4 hrs) going easy on the motor.  Clearance measured the same. Then on the 3rd day I went hard on the motor and revs, and the valve pull up to zero clearance after about 15 minutes. Now it has two new OEM Ti intake valves installed and runs great.  Head seats looked excellent.

I rided 2 hours since no problem, I will check clearance soon again. If I have to shim too often i will change the valve when top end will be due

Is it better to change all valves , intake ones or only the one thats worn out?

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I rided 2 hours since no problem, I will check clearance soon again. If I have to shim too often i will change the valve when top end will be due



Is it better to change all valves , intake ones or only the one thats worn out?
If a valve pulls up to zero clearance twice, then you need to replace it. Don't wait until the piston is due. The bike won't kick start with the worn valve, plus you risk serious damage.
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I rided 2 hours since no problem, I will check clearance soon again. If I have to shim too often i will change the valve when top end will be due



Is it better to change all valves , intake ones or only the one thats worn out?


If you are a casual recreation rider, just replace the one valve that is worn out and carry on having fun. If you are in competition, a racer, replace them all together as a set.

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