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What happens when a timing chain is too slack?

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Hi

I have a yamaha tt350, i have had this problem which is getting worse, if i hold the throttle constant in the mid range revs there is a really harsh sounding vibration, and its missing a little, but its not there at idle and it goes away when you twist on the throttle .

The plug always shows a really rich colour. I have tried every possible jetting combo, and made it rediculously lean and it still vibrates at those revs. I have also checked the timing marks and it all lines up.

So the fact that it has a funny vibration in the mid range, is rich and misses a bit made me think maybe this vibration is caused by something mechanical, and the missing is a electrical problem being caused by the vibes.

The engine was rebuilt about 6 months before i bought it, so i decided to take the side cover off last night to make sure the balancers marks all lined up and they were fine too. While in there i noticed the timing chain moved quite a bit when you push on it.:applause:

So my question is can a loose timing change have such a dramatic effect at only one point in the rev range, and could the looseness of the chaincontribute to putting the timing out so much that it will have complete misses?

Thanks:worthy:

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I had the automatic tensioner crap out on my XR600. The first symptom that I noticed was poor running. I noticed it mostly at idle and low revs. I thought that I had a burned valve. Eventually it got loose enough that I could hear the chain slapping around. I replaced the chain and the tensioner and all was well.

On mine the failed tensioner only had problems when the engine was hot and running. When I opened it up the cam chain was tight.

If your problem is the cam chain do try something. When it gets bad enough it will grind against the cases. That puts metal bits in the oil. It can skip a tooth or just break or come off. That will result in the piston meeting the valves.

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Time for a new chain and tensioner, dont ride until you do this becuase when it breaks piston and valves will deffinetly have an inprompto meeting together

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yeah i haven't been riding it,

i've been using every spare minute i have since xmas testing out all the jetting timing etc, i checked the chain tension in cylinder cover and it seemed fine, but when i checked it down the bottom it moved alot more than i expected. so in the last 2 months i have only had the engine running enough to check if i had fixed it.

thanks

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