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Old 04-03-2012, 06:30   #1
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Yanmar 3GM Fuel Pump Lever Operation

I've just unintentionally added an on-engine Yanmar 3GM30F fuel lift pump to my on-board spares because I did not know the "feel" of the manual pump lever. I've read the book and several threads about bleeding the engine and do, in fact, use the off-engine electric fuel pump to bleed the lines. However, my lack of experience caused me to erroneously believe the pump was defective, when the problem was actually operator error. :bang head: I wanted to know that the on-engine pump does work (I'm fighting a hard cold-start condition discussed elsewhere).

To the point, what feels like the stroke of the lever isn't! It's only after the lever has bottomed out that there is 1/8"-1/4" more travel that really does the pumping. If you operate the lever, as I did, across what feels like a normal range of motion, you'll get zero pumping action. It's only when you give the lever this extra push at the bottom of it's apparent range that it actually pumps fuel.



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Old 04-03-2012, 06:39   #2
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Re: Yanmar 3GM Fuel Pump Lever Operation

I noticed this as well on my perkins prima 50 fuel lift pump. Definitely good to know and see when you are not rocking and rolling. Had to order an extra lift pump anyways because the small gauze filter which needed replacing was not sold seperately. Now I have a new spare in case the original fails.

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Old 04-03-2012, 11:26   #3
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Re: Yanmar 3GM Fuel Pump Lever Operation

Thanks for sharing your hard won experience, Jim. Good tip!

On some engines, the line to the injector will not bleed unless the throttle is advanced slightly (1/2). If you do not open the throttle, no fuel will be delivered to the injector, and the line cannot be bled.
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Old 04-03-2012, 14:04   #4
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Re: Yanmar 3GM Fuel Pump Lever Operation

Another tip I learned in a engine rebuilt class: The pump may be in a partial pump cycle depending on the position of the lobe on the crank shaft and where the pump lifter arm is positioned. Sometimes it helps of you momentarly crank the engine so the crank rotates a bit and the pump lifter arm is them free and not in a half up position. This gives the manual lever a full travel range and provides for more pump action. We don't bleed often so we don't remember from one time to the next how far the manual lever should travel when you are manually pumping it.

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