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Old 03-03-2013, 05:25   #1
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Yanmar excessive no load rpm?

I just surveyed and sea trailed a boat and am wondering why a Yanmar 4JH2TE would turn up to 4600 rpm with no load and only 3100 WOT under load. There are a variety of reasons I can think of to cause it to not turn up to 3600 under load, but what causes the no load rpm to be too high. Governor setting? Injector issues?
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Old 03-03-2013, 07:42   #2
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Re: Yanmar excessive no load rpm?

If that is a 3,600 rpm engine, then no load rpm should be less than 4,000. The governor is the problem.

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Old 03-03-2013, 08:09   #3
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Or the tack may be off
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Old 03-03-2013, 08:17   #4
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Re: Yanmar excessive no load rpm?

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Or the tack may be off
Yanmar TACHOMETERS usually read about 100rpm too high at maximum rpm, but not as high as he's reporting.

Perhaps a throttle cable adjustment?
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Old 03-03-2013, 08:29   #5
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Re: Yanmar excessive no load rpm?

Max no load RPM on most yanmars is 3800. I had my tach checked with a strobe and it indicates about 200 rpm high, but 800 rpm high seems very unlikely. Seems to me the governor is bad.
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Old 03-03-2013, 12:39   #6
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The numbers I gave are from a photo tach. They are actual RPM. Is it just a governor adjustment or could it be more serious. Is it possible a seller may have intentionally adjusted the governor to mask another issue? How else could it be off by so much?
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Old 03-03-2013, 13:28   #7
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Re: Yanmar excessive no load rpm?

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The numbers I gave are from a photo tach. They are actual RPM. Is it just a governor adjustment or could it be more serious. Is it possible a seller may have intentionally adjusted the governor to mask another issue? How else could it be off by so much?
I'm not an expert by any means, but I don't see how a maladjusted governor high end limit could be used to mask anything. However, it certainly could allow the engine to be damaged. Is the idle RPM about right?
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Old 03-03-2013, 13:56   #8
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The engine idles fine, does not smoke and runs well. The only issues are no load rpm too high and WOT rpm under load are too low. I think I can attribute the wot issue to being over propped. Also, the engine has dual 100 amp alternators which I assume are adding to the load. Is adjusting the governor a complicated job for a Yanmar tech only, or is a simple thing.
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Old 03-03-2013, 14:18   #9
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Re: Yanmar excessive no load rpm?

Not familiar with that model, but on the GM there are two limiters. No load maximum speed limiter is an adjustment that prevents the engine from over revving. It sets the maximum you can move the throttle. The fuel injection limiter limits how far the fuel rack actually travels, so if over propped and throttle is set to go faster, you can't put more fuel in than is desired for destroying engine, and rpm will be lower due to excessive load.
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Old 04-03-2013, 14:38   #10
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Does anyone know how to adjust the governor on a 4 JH Yanmar.
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Old 04-03-2013, 14:48   #11
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Re: Yanmar excessive no load rpm?

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Does anyone know how to adjust the governor on a 4 JH Yanmar.
I don't. Google search found the service manual though. Thinking more about this, unless the no load adjustment has been found to have rattled itself nearly off, I would think that something in the governer broke or fell off to be that far out.

http://sagaforumet.com/yanmar-manual...kapittel_3.pdf
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Old 05-03-2013, 06:26   #12
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Re: Yanmar excessive no load rpm?

Thanks for the link!
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