FYI: Found fix to potential stall problem on YSM8 & likely many other Yanmars diesel engines-
I have had intermittent problems with my older YSM8 single cylinder Yanmar diesel stalling out under load after 5-10 minutes of running.
After pumping and cleaning the fuel tank, replacing numerous filters and trouble shooting - the problem was found in the fuel pickup tube. Yanmar, or S-2 the sailboat manufacturer inserted a very fine mesh screen inside the fuel pickup tube at the end of tube (at bottom of tank) - which cloggs easily.
I believe that it was placed there with good intentions - to prevent fuel sludge/ gunk from entering the fuel injection delivery - but this filter - screen can easily clog and starve the motor for fuel, until it stalls out completely. This usually occurs not at the dock or during warm up, but under load when the engine has run for 5 - 10 minutes, and then cuts out right when you need it. This problem can mask itself as many other problems- -I thought that the fuel was bad - pumped it out - then mechanic thought it was the fuel lifting pump - which was old but still O.K. Finally a third mechanic found the problem, and after the completely clogged screen was removed - the engine runs again like a champ! I have read several other posts in the past year of other Yanmar owners stating similar problems with stalling, low power under load, intermittent failure of engine, hard starting etc. Please check for this potentially clogged fuel filter - screen at fuel pickup tube in your fuel tank! It can be a potential source of major trouble or engine failure -and it is a hidden problem that most sailors will not think of. I didn't even know that this fuel screen existed - it is not listed in the Yanmar parts lists -as may of their engines didn't come with fuel tanks. PLEASE PASS THIS INFO ON TO ANY OTHER YANMAR OR DIESEL ENGINE OWNERS. This simple fix can save you major aggravation and wasted $$ replacing parts that aren't necessary. I can recall another sailor stating the same problems with his YSM8 and reporting to be replacing the entire engine/ rebuild that may not have been necessary.
My experience with all diesels over 20 years is that bad fuel, fuel delivery, clogged fillters or air leaks in system is the cause of most diesel engine problems. Yanmars and most diesel are normally very reliable, but a lack of adequate fuel or pressure will cause stalling every time.