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CRF250 07 strange engine noise, cam chain, tentioner?

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Hello everyone. I am new to these forums and I'm foreign so please don't be so harsh on me  (language wise) ;)
So I recently bought a 4 stroker crf250 07.
I noticed a strange noise, when the bike is at low idle it starts making this noise: video:

https://www.youtube.com/watch?v=bRQKAVgcQ3E

It sound to me like a decompression valve engaging.. AS you can see when you bring up the rpms the sound goes away, could it be it?
Another problem I have is when the engine is TDC ( top dead center) the cam marks dont line up. video:

https://www.youtube.com/watch?v=6hqhCzTimmo

I took out the cam chain and when compared to the new OEM one it was almost the same maybe only 1-2mm streched.. ( Is this enought for the marks to not line up?)
The tentioner is in good conditon its really working well ( I believe).
Any suggestions or ideas on do I need to change the cam chain or tentioner or I could keep it this way?

Technical info:
Piston and crank has around 8 hours on it.
Valves shimmed to spec.
Starts first kick everytime.
Boggs a bit but It maybe because of a way to rich pilot jet. (otherwise rides great!)

Simon,

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Take the head off, release tension on the cam chain and remove cam stays (the half circles that hold the cam in place). Slide the left cam bearing toward the sprocket and lift timing chain off of the cam. Turn the gear in the right inspection hole with an Allen wrench until the two TDC indicators line up and then reinstall the cam without turning the timing chain, Cam lobes pointing up and back and the lines on the cam sprocket even with head. Now your timing should be right.

That noise sounds like a loose timing chain to me. The decomp lever should only click on the kick start revolution and then stay out of the way while the bike it running. The tensioner doesn't really just go bad, as long as it springs back into place well it should be ok.

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Simon, if your bike starts first kick and runs great  your timing and jetting are fine , don't  F with it. And that noise sounds normal to me , mines an 07 with very low hours on it and it sounds the same. I know my tensioner is working fine an my chain isn't stretched because I checked my cam timing with a degree wheel and dial indicator and it's right on. 

 

Those timing marks can seem a half tooth out one way or an other. If they were out your bike would not run great!

Edited by bucket list
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My 2013 250r makes that same noise right before it stalls. My dads 2012 250x makes the same noise right before it stalls too. think that notice is normal

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My 2013 250r makes that same noise right before it stalls. My dads 2012 250x makes the same noise right before it stalls too. think that notice is normal

 

Ya, at very low idle speeds theres some gear clatter that he's probably hearing,    normal.

Edited by bucket list
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If I were you I wouldn't mess with it. Because if your like me I mess stuff up when I try to fix it lol

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The book calls for the idle to be set at 1700 rpm. It sounds too low to me and centrifugal force moves the decompressor out of the way. Try turning up your idle a bit and see if the noise goes away. I agree with those who already posted, if it starts first kick and runs good leave it alone. Many problems are introduced by owners. And yer English ain't so bad either.

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