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YS 120 ???

Old 07-31-2010, 04:13 AM
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DennisS
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Default YS 120 ???

I have an older YS 120 that always ran like a top. It sat up for a while (lubricated) and now has alomost no compression. Thoughts, ideas appreciated.
Old 07-31-2010, 12:45 PM
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ChuckW
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Default RE: YS 120 ???

Sounds like either a stuck valve or ring. I'd put my money on the stuck valve; it is common on engines that sit..

Pop the rocker cover off and see if one of them is stuck down. A little penetrating oil and pushing on them a few times will often free them up.

If that's not it, put a few drops of oil in the cylinder through the glow plug hole and turn it over a few times.
Old 07-31-2010, 01:18 PM
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Gray Beard
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Default RE: YS 120 ???

And you are never to use petroleum products in a YS, they play havoc with the diaphragms. At this point I would do what Chuck says then order up a couple of new diaphragms and gaskets for it. When something goes wrong with a YS and it starts running bad then the diaphragm is usually the problem.
Old 07-31-2010, 03:45 PM
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ChuckW
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Default RE: YS 120 ???

I have one on the bench right now that I am rebuilding for someone. Several o-rings look like they've been eaten with some sort of chemical. Not sure what did it. some sort of cleaner maybe?

I recommended penetrating oil earlier for freeing up a stuck valve. A few drops of fuel might be a better option.
Old 07-31-2010, 08:04 PM
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MikeL
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Default RE: YS 120 ???

Fuel is a much better option for a YS.  Like GB says, petroleum will eat the "soft" parts of a YS.  Chuck, it's possible that you're seeing the effects of using a petroleum-based after run oil.
Old 07-31-2010, 09:27 PM
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ChuckW
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Default RE: YS 120 ???

Yeah, I'm not sure what got to it but something sure did. It wouldn't run worth a crap with all those leaks. It's all sealed up now, good as new and ready to give back to the owner.

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