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s/v Ubiquitous
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Discussion Starter #1
I am sure this topic has been discussed but I have not found it in the search so here it is again, my apologies for redundancy. I have an 80s model Yanmar YSM 12. Been a great motor for the last two years, always cranked and ran like a dream. I had to re-thread the return line (small metal tube coming from the injector) because the hole in the filter housing striped. That done I re installed, bled the lines and she popped off today. Needless to say I was ecstatic until throttled her up and she became erratic and eventually dying out. She continues to start and will idle without trouble but as soon as I throttle up she revs, loses her momentum and dies again. I have bled the lines many times and have never had this problem before, like I said she ran like a champ. Have I missed something?

Update

Aggravated, the fuel system on this motor is not rocket science. I have tapped and put helicoils into the top (return line threaded hole and the bleeder hole) making sure both are tightened down with banjo washers top and bottom on the return line and one on the bleeder screw. I have bled the lines up to and back from the injector. Thinking everything would be right as rain I cranked it up (cranks easy). Then I went to throttle it up and the same thing is happening, at higher rps it wants to quit on me. It will idle all day long without a miss but once I put some rpm's behind it it begins to rev up then poops out.

So question...how can I find the leak if it is in fact in the housing. I am assuming the leak is pulling air IN TO the filter and not spewing out as I would be able to see fuel coming out. I would think it bad to try the soapy water treatment looking for air being pushed out. She is so close to running like the dream she has always been. Aggravated.
 

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Senior Member
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As a test you might insert an outboard type 'squeeze bulb' in the line and pump it up.. any leaks would show then as 'leaks', not sneaky air sucker-inners ;)

High odds that despite the bleeding it's not done yet, but if there's air ingress that's what you need to find first.
 

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s/v Ubiquitous
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Discussion Starter #6
bleeding

Okay this may seem like a dumb question but in what order do you go through and bleed the fuel system. I have been going from the fuel filter to the injector and then back in that order bleeding each banjo fitting as I got to it.
 

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Re: bleeding

Okay this may seem like a dumb question but in what order do you go through and bleed the fuel system. I have been going from the fuel filter to the injector and then back in that order bleeding each banjo fitting as I got to it.
Start at your lift pump and go downstream. Close off the water valve for prolonged cranking.

The filter sounds suspect. Maybe all new gaskets & O rings. If there is any air space visible in the filter glass, it is likely leaking there.

Maybe dirt or debris on the mating surfaces

Some lift pumps may have an integral filter/screen

Maybe try an outboard tank with fresh fuel, probably a stretch though

As mentioned, pressurizing the system with a bulb or electric pump from the tank outlet downstream will probably show where the air leak is.

Make sure the tank is venting properly

Let us know what you find

Paul T
 

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s/v Ubiquitous
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Discussion Starter #8
She's running, Sea Trial tomorrow (taking her out in the bay) I still think there is a bubble or two lurking around but as it stands I have no air or fuel leaks and she holds RPM throughout throttle range. Thank you all for the guidence. Ended up just needing fully bled. Zero dollars YEAH!
 

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She's running, Sea Trial tomorrow (taking her out in the bay) I still think there is a bubble or two lurking around but as it stands I have no air or fuel leaks and she holds RPM throughout throttle range. Thank you all for the guidence. Ended up just needing fully bled. Zero dollars YEAH!
Life is good!!, thanks for the feedback.

Paul T
 
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