Yanmar loses RPM in gear - SailNet Community
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post #1 of 23 Old 11-26-2013 Thread Starter
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Yanmar loses RPM in gear

I have about 500 hours on my 3GY20 Yanmar. I've had no problem with it. I've always been able to run it up to 3400 - 3600 RPM. I prefer to run it about 2700 RPM for comfort and vibration, and that seems to optimize speed/efficiency. I try to run it at 3000 periodically to clean the cylinders.

Today I was running it in the bay about 2500 RPM, pushed it up to 2800 as I headed back to the marina. I felt it slow down, looked down at the tach and it was 2500 again. Increasing the throttle made no difference--it wouldn't go past 2500. I can put it in neutral and rev it to 3800, but in gear nothing past 2500.

Any ideas where to start looking?

Thanks.

Steve
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post #2 of 23 Old 11-26-2013 Thread Starter
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Re: Yanmar loses RPM in gear

I should add that I can see the prop in the water and it doesn't have anything wound around it. At least nothing that's visible.
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post #3 of 23 Old 11-26-2013
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Re: Yanmar loses RPM in gear

When was the last time you changed a fuel filter?? Could be the early sign of pluggage.. If that's not the issue for sure, perhaps your fuel tank pickup has a screen and it's starting to get gummed up..

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post #4 of 23 Old 11-26-2013
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Re: Yanmar loses RPM in gear

Dirty bottom or shaft if there is also black smoke.
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post #5 of 23 Old 11-26-2013
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Re: Yanmar loses RPM in gear

Fuel starvation probable
Low compression possible

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post #6 of 23 Old 11-26-2013
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Re: Yanmar loses RPM in gear

I concur likely fuel problem filter or possible injector issue check filter then lift pump lastly the injectors

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Re: Yanmar loses RPM in gear

I also think it sounds like fuel starvation.

When was the last fuel filter change? If the filter is dirty or fills with water the engine will begin to lose power and be unable to achieve full RPM.

Might check the fuel pickup clear (blow it out using LP air?). Check for a kink in a fuel line.

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post #8 of 23 Old 11-26-2013
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Re: Yanmar loses RPM in gear

Steve,

Once you have checked out the fuel supply, check your exhaust mixing elbow.

It clogs up slowly over time and restricts the engine due to back pressure buildup.



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Re: Yanmar loses RPM in gear

What was the exhaust like when you only achieved 2500 rpm in gear? Any black smoke or soot? If so the exhaust elbow's restriction is a likely reason.

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Re: Yanmar loses RPM in gear

I just serviced one of our charter boats a 3ym30, it had the same issue, I sent the injectors out to be serviced and replaced exhaust elbow now it runs like a champ

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