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I am glad you got this far.
On a Yanmar with a water sensor inside the fuel filter housing, it is always best to remove the two bolts securing the filter housing to the motor, then unscrew the housing from the plastic nut without turning the nut and twisting the wires. As soon as you begin to loosen the housing from the nut fuel will begin to run out through the plastic hose...be prepared.
My guess is that you did not place the O Ring at the bottom of the fuel filter. Possibly you did and it is not seated properly, or maybe you forgot to properly lubricate the O ring. It is also possible that one of the wires are in the nut threads.
There should be zero diesel leaking from any point on your engine.
I hope this helps you. Let me know if it does.
Bill BeBe 387
Thanks for the good advice. It turned out to be an air leak in the bottom of the primary filter. I removed, cleaned, and carefully threaded bottom water sensor on (being careful not to damage wires) then opened bleed screw and to remove air and motor now runs well.
When Bill said it was near impossible to pump primer when bleed screw is tight, I realized the problem. I could pump and fuel was escaping through threads in water sensor cap.
If you can pump the manual pump on top of the fuel filter housing on the Yanmar, you probably have not sealed the filter and you are sucking air which is causing your problem. When the filter is installed correctly, it is near impossible to pump that manual pump unless you open the screw that Mark describes.
It is a little tricky to replace that fuel filter because of the wires that go to the sensor at the plastic nut at the bottom of the of the filter assembly. If you try to unscrew and screw that nylon nut, you may damage the wires, twist the wires, and/or get them into the treads. Loosen the entire assembly from the motor mount, then turn the assembly holding the nut stationary. As soon as you complete about 1 turn, fuel will begin to drain from the drain hose which is about 1 foot long and attached to a fitting on the nut. The drain hose gets brittle and may have fallen off...if so, replace it. To remove the filter from the assembly continue to turn until the plastic nut is loose from the bottom of the filter...reverse the process when placing a new filter. Use the drain hose to capture most of the fuel. Protect the 175amp alternator from fuel spills. When everything is back together, open the vent screw (purple or blue) and pump until no air is coming out. Remember, if you have a dual Racor, the point on the short tip of the valve handle points to the active filter...NOT the long handle.
It is possible that after you do the above correctly that you will need to bleed each of the injectors as Mark described. Be sure that you do not fill up the muffler with salt water. It is best that you have some experience with you when you do this the first time.
I bet that there is a youtube video of this out there. I did a search on "Yanmar fuel filter replacement" and saw several that may help you. The real issue for you is probably the wires on the nut at the bottom of the filter assembly.
I hope this helps.
Pitons, St. Lucia