I have an old Yanmar SB12 single cylinder diesel that dies on me roughly 3-5 running hours after I bleed the fuel system. This has happened a few times, and i've been lucky to be able to sail to safety... i don't want it to happen again. Each time it dies, all that needs to be done is to bleed the primar, then secondary filter (never bled the high pressure lines) and she starts right up again for another few hours of run time.
I am almost positive there is an air leak somewhere in the system. The fuel system is as follows: Standpipe -> primary filter (racore R12S) -> mechanical pump with priming bulb -> secondary filter -> high pressure injector pump -> injector -> return line to secondary filter.
There was a note on the service manual cover from the previous owner that said "replace metal lines." That was the year the pulled the boat and it wasn't used again till I bought it last year. The metal lines have not been replaced, but there is no evidence fuel spraying from these lines during operation - why else would those lines need to be replaced??
How can one find the location of an air leak?
How do you test fuel filters for air leaks?