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Old 03-11-2008, 09:10   #1
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Yanmar RPM Woes

When out for a sail yesterday my Yanmar 2GMF started having problem maintaining RPM's. It would oscillate up and down between 2000 and 2500 rpm. Iím assuming itís time to change the filters or I got some air in the line when I bled the water out of the water separator. But I also read that Yanmar used to put a screen on the fuel pick-up. Before I go and pull the pick-up, does anyone know when Yanmar stopped doing that?

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Paul
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Old 03-11-2008, 12:27   #2
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I would imagine that the boatbuilder would have done that, since Yanmar only built the engine, and not the fuel storage & delivery system.
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Old 03-11-2008, 13:05   #3
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Where did you read that Yanmar put screens in the tank pick up tube?
Yanmar didn't build the tank which most probably does have a screen but if you recently bled the system and never before had a problem, I suspect the problem is self-evident
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Old 03-11-2008, 13:11   #4
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The problem is indeed self evident --- the engine speed cycles. What the asker is looking for is a solution, and the solution apparently is not self evident to him. Perhaps providing the self-evident solution might be more helpful.
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Old 03-11-2008, 13:31   #5
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how long has it been since you changed the fuel filters??
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Old 03-11-2008, 13:37   #6
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Yanmar RPM Woes

Thanks all, I think. I found the reference to the pickup screen right here.

problem with yanmar diesel

It is evident that there is a problem and most likely filters or air. At the same time I would like to save myself the effort if there is no screen on the pickup tube. If there is a screen, it seems like the first place to start.
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Old 03-11-2008, 13:39   #7
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Aloha Paul,
I wouldn't think air in the system would make the oscillation (hunting) symptoms. More likely it is fuel or a speed adjustment at the injection pump. I would, as you suggest, change the fuel filters, rebleed the system and try again. Usually if there is air in the system it won't start.
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Old 03-11-2008, 13:40   #8
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I changes the filters about a year ago. Good chance the hurricane stirred up the tank a bit.
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Old 03-11-2008, 18:12   #9
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Do you have primary and secondary filters?
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Old 03-11-2008, 21:01   #10
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As grandma used to say, "Go fix the last thing you 'effed up."

If you bled the system recently to remove water -

- Did you get all the water out?
- Did you let air in?
- Did you let debris in?
- Did you determine where the water came from?

Before rebuilding the fuel tank or the injection system I would go back and completely redo the bleeding process. I would also add new filters because they are cheap and decent medicine.
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Old 03-11-2008, 21:10   #11
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Start with your filters. I change mine every 8-9 months. If you're in lumpy water and the fuel tank is old, my money is on the filter.

Spend 6 bucks and 10 minutes to change it.
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Old 03-11-2008, 22:31   #12
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I had a yanmar 20 in a boat i used to own. i was cautioned by the previous owner that i should have the fuel system polished and soon found out why, during a shake down run before sailing her around Michigan i lost power. same as you. when i removed the fuel fill cap i heard a suction noise and found the tank vent to be clogged, months after correcting i had the same problem again during a storm on lake Huron, with no new filters on board i found that you can remove the inlet hose on the lift (fuel) pump on the starboard side and use your oil change suction pump in reverse to blow the lines out with air and push any slime off and out of the fuel sock and then use it to suck fuel up to the pump, this works well to get you going again when in a pinch.
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Old 04-11-2008, 10:21   #13
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Yanmar RPM Woes

Thanks all. I have both a primary/water seperator and a secondary filter. Will change both this weekend. Also check the vent on the fuel tank.

Paul
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Old 04-11-2008, 11:35   #14
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If you do have a screen on the fuel pickup take it off and save yourself some trouble.
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Old 09-11-2008, 21:38   #15
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Black with Bugs

I removed the primary filter and it was black with bugs along with the water separator. I replaced the primary with a 2 um, which kind of makes the secondary useless. I was going to use 10 um, but forgot the wrench I couldn't open the canister for the secondary. The vent line was clear and the pick-up was free of any resistance in or out. The engine ran well. The question now is, the best way to treat the tank?

Paul
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