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Heres a strange problem for the community, I have a bike thats failing a compression test but passes a leak down with flying colors...

2012 KTM 250 SX-F 

Valves spot on, clearances spot on

New cam chain

Dirt Tricks cam chain tensioner 

HAS fuel 

HAS spark 

4% leakdown on the leakdown test 

FAILS compression test horribly 

Thoughts?? 

I am flat out stumped... 

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What are the compression specs and what are your actual readings?

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Were you compression testing with the throttle held open?  If not, that's probably it.  If so, try another compression tester.

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Compression texting was done by a KTM tech, the reading was 15 psi and we tried two different testers to make sure. 

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49 minutes ago, jase12 said:

Compression texting was done by a KTM tech, the reading was 15 psi and we tried two different testers to make sure. 

I take it , the bike does not run, it wont at 15 psi. so if it runs, theres something wrong with your compression test.

 

also how much pressure were you using for leak down test?

Edited by Spud786
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Incorrect valve timing or wrong year or model piston (low piston crown).

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On 1/21/2019 at 7:07 PM, Spud786 said:

I take it , the bike does not run, it wont at 15 psi. so if it runs, theres something wrong with your compression test.

 

also how much pressure were you using for leak down test?

Correct it does not run. Not sure on the pressure like I said the KTM tech just did his thing and I watched. lol 

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