Engine stall

My IP380 has got a very well taken care of Yanmar 4JH2E. We started the engine and were cruising at about 1100rpm (my most efficient level before that annoying high pitching sound appears). After 20 minutes running nicely the engine lost about 200 rpm at once, I went immediately in idle assuming I caught something in the propeller (which was not the case) and then the engine stalled. Attempts to restart it resulted in running for 2 seconds and then it stalled again.
This could be either air in the system or a fuel feeding problem.
Since after pulling the small fuel back feed hose from the fuel filter and then cranking the engine did show only two tiny drops coming out of the pulled back feed hose, instead of the expected squirting, it is assumed the problem is in the fuel line. Either the fuel pump died from one moment to the next, or the fuel line is blocked somewhere.
Before disassembling the fuel pump I’d prefer to check the whole fuel line. The filters appear ok, just a little bit of dirt on the bottom of the Racor water separator, however no water at all.
Does this mean the fuel line is clean?
I read in a forum that sometimes they put a strainer at the entry end of the fuel line in the fuel tank, and that strainer can get clogged. The fuel tank gauge is working and shows about 70% full. Here my questions:
a) Did Island Packet put strainers in at the beginning of the fuel line (must be way down in the tank)? (IP did not answer my email regarding this)
b) If so, could such a strainer clog so quickly that nothing goes through anymore from one moment to the next? Note: after each 10 hours of running at low rpms I bring the engine for a few minutes above 2500 rpm as suggested by the Yanmar manual. This went always without any problems.
c) Any other thoughts or suggestions?

Thank you!

Martin

Update and
answer to question a): I found a very nice and responsive guy at Island Packet: Robin Lewis, Parts Department, This email address is being protected from spambots. You need JavaScript enabled to view it., Tel. (727) 535-6431, who confirmed that there are no strainers built in the fuel pipe down in the fuel tank, however, if anybody would prefer getting one, they should contact the manufacturer of the fuel tank, Rhonda at Ezell Manufacturing, Tel. 850-578-2558.

answer to question b): n/a

The problem was indeed a clogged Racor filter due to water/dirt in the tank. The viewing glass of the filter showed no water and just a tiny bit of dirt. So I could not assume the entire filter was totally clogged as it turned out to be. This is even more surprising since all fuel is filtered before it goes into the tank. Apparently even for idle there was not enough fuel going through! As a conclusion I take that a clogged filter can stall the engine without any prewarning.

Hi Martin, We have a vacuum gauge on our Racor filter. If the filter is clogged, the gauge shows a greater vacuum to pull the fuel thru the filter. Our gauge also shows Yellow (caution), Red (too high - over 5psi or so as I recall) We change Racor if in the Yellow, and keep lots on board - 2 micron. Keeps things clean.
That said, we did have a stalled engine problem. Mechanic traced it to clogged shutoff valve, right after elbow on top of the tank. Valve diam was about 1/8 inch. I didn't realize that you can remove the fuel hose at the tank, and there is no back flow or fuel spill - thus waited for mechanic. Clog was some algea sort of glop. Easily cleared and engine ran fine.
Good to hear you fixed your problem.
Fair winds (or motoring) Drew

Thank you Drew, very valuable information about that shutoff valve! I understand this is not that small tap by which you can shutoff the fuel pipe manually (see picture), but a second one higher up the fuel pipe which cannot be seen nor assumed.
Fair winds, Martin

Hello Martin,
We have an IP380 also. Not sure how old yours is, but ours is a 2001 model.
You may want to consider Fuel Polishing your tank. Over the years, with what can “grow” in there, the bottom of the tank can get goopy.
We had this done prior to some extended long range sailing, and was quite pleased with the result, and had no issues. If you have been operating in rougher waters, the stuff can get stirred up pretty good and very quickly clog the lines and filter.
Cheers, Dave