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Old 06-11-2010
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Question Yanmar YSM12 Keeps Dying

I have a YSM12R that has been giving me problems since the start of the season. As we were leaving the marina where it was stored for the winter and where the mechanics commissioned it for the summer, the engine died. I bled the lines and the engine restarted and we sailed to where I keep the boat for the summer. As we headed in, the engine wouldn't start, bleeding or no.

The marina sent someone over to check it out and the theory was they'd over-filled the oil, which got into the cylinder as we heeled. They siphoned some out and the engine ran fine.

A few days later I ran the engine for about 30 minutes at the dock, no prob. As we headed out for a Wednesday night race, it died and wouldn't stay running. It'd fire but not stay going.

Since then I've gotten various suggestions, and have re-seated the secondary filter and replaced the fuel lines into the Racor and from Racor to the secondary. Engine ran like a charm in neutral and under load for over an hour, stopped and restarted no problems. Today, same thing - stopped and started, under load and in neutral, all fine. Until I ran it in neutral at fairly high RPMs, then throttled back fairly quickly and the engine died. Wouldn't restart until I bled it again. Then it seemed fine until I did the same thing - throttle up, throttle back and it died and wouldn't stay running.

I bled it again and if I throttled back slowly it seemed not to cause the problem. Of course, it's like the old joke where the doctor says, "Don't do that again." But I'm concerned about whether there's something else I should be looking at or if this is more or less normal behavior.

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Old 06-11-2010
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A vacuum gauge would tell you a lot. One problem that is difficult to diagnose is a chunk of debris plugging the pickup tube in the fuel tank. Things work fine and then the engine quits, when the vacuum drops the debris falls out of the way and the engine runs again. It is often overlooked by most mechanics. High vacuum generally causes air getting in the fuel from an o-ring on the filter or somewhere else. A vacuum gauge would help diagnose.


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Old 06-12-2010
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Sounds like it is a fuel problem up stream of the engine. I had problems like that and finally pulled the fuel tank and had it cleaned & replaced all hoses and fittings. Good luck.
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