Question about 1980 Yamaha XS 650 G

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Can't find compression specs for 1980 Yamaha 650G

Restoring this bike, I can't find what the compression should be. I ran a compression test and originally got 120 psi, then I put a little oil in the cylinders and got 240 psi. The engine will not pop with 120 but it did pop ( a little) with 240. Please help.

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  • kirsten689 Jul 13, 2009

    Thanks for the tip. I dug in further, and the valves were adjusted wrong, the camchain was loose and the timing was off. Now I just have to rebuild the carbs, It's got Mikuni Kogyo carbs on it but no part number, very frustrating.



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  • Yamaha Master
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The compression should be around 150psi, but at 120psi it should pop, try to readjust the valve clearance.
Hope this helps!

Posted on Jun 21, 2009


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