Engine Stalling and furl filters are nearly dry?

[Dgort]

I am working on our yacht clubs boat, 1959 40' USCG Utility. We have been having engines stall, twin 671's, on us and cannot figure out the issue. Installed Racor filters this year that are rated for 2x the flow needed ahead of the primary and secondary filters. We thought that this would improve things but the engines are still stalling. Each time one of the engines stalls, we remove the primary and secondary filters and they have less than 1/4 full of fuel. We top off the filter and screw it back on and the engine starts. Last time I did this, we ran it at the dock at a high idle rpm for 40 minutes and then took it out on the lake for another 45 minutes. no issues... Until last night when the port engine stalled... Looking for suggestions. but really would like to understand why the primary and secondary filters are being sucked dry. I attached a diagram of the fuel delivery plumbing for the port engine.

Thanks for your help.

Dale G.

 

[AllDodge]

Welcome
Look at the tank pickup tube and if it has a antisiphon valve that may be clogged. Also look to see if fuel line is collapsing

 

[jgmo]

Hi,
Agree that this could be caused by an pickup tube problem. I've seen them cracked, or with a hole in them and sometimes just snapped off.

In the case of a hole in the tube or one that's broken off, the problem will occur consistently each time the fuel level drops below the damage. A crack however can "flex open" at varying times and cause the problem to be a bit more unpredictable.

Something, like a towel or rag, floating around in the tank can cause this too.

A suction air leak will also cause this. Taking the return line off at the tank and putting it into a bucket of clean fuel is known as a "spill back test" and can be used to identify low return volume and whether or not air is being pulled into the system by the appearance of bubbles.
A common source of air entering the fuel is a poorly seated/sealed primary fuel filter. I have also seen spin on type filters with tiny pinhole in them from shipping or rough handling.

Remember, if there's air in the fuel it will ONLY enter on the SUCTION side of the pump so don't bother looking at the delivery side.

Good luck.