Yanmar YSM-8 Trouble

[rjg23]

I have a 1979 PY-26 with an inboard Yanmar YSM-8 diesel engine.

On a recent trip we were heading down river with current and outgoing tide into wind and swell. Needless to say we were powering into pretty heavy chop but doing alright. After having left the mouth of the river, into calmer waters, we continued to power along and about a half hour later the engine died. Seemed as if the fuel ran out. I filled the tank, didn't take much, and powered back up and ran for another 5 minutes and died.

This is now the constant: instant starting, 30 minutes of smooth running, then dies. If left alone for a while I'm able to get another short period out of it.

I've changed fuel filters, put new fuel in, checked fuel tank vent hose, and run the engine with the fuel cap off (with the hope that it would allow the fuel to flow to the engine more easily).

Any suggestions before I drop a ton of money to have it looked by a professional.

Thanks

[Faster]

Fuel cap on or off shouldn't make a difference... you're tank will be vented elsewhere, and you are risking contamination of your fuel by doing leaving the cap off.

Sounds like an air infiltration issue to me... check all your connections and bleeders. Many fuel systems are under vacuum while running, so leaks don't show as a fuel drip, but air can get sucked in while running. When stopped, your air bubble works its way to a high point, then when started eventurally makes it to the injector pump and it quits....