John...here are the steps...
BLEEDING THE FUEL SYSTEM
(Purging of air which causes shutdown)
This bulletin contains helpful information for bleeding the fuel system of a Yanmar Diesel and other
small diesels as well. Please post where your field service personnel can review.
Since the presence of air in the fuel system anywhere between the fuel tank and the injector will
"use a no start or erratic running condition, always bleed the air from the system when the fuel
system is disassembled, filter changed or run out of fuel.
1. Make sure fuel tank off is in "on" position.
2. Bleed the air from fuel filter. Loosen the air bleed screw at the top of the fuel filter body and
operate the manual handle the lift pump until the air bubbles completely expel in the fuel flowing
from the filter.
3. Bleed the air from the fuel return pipe. Loosen the connector bolt of the fuel return pipe installed
on the fuel injector, and bleed the air by operating the manual handle of the lift pump. (If there is
more than one injector, bleed the one at the end of the line).
4. Bleeding the air from the fuel line - (line from the filter to the injector pump). Loosen the air
venting screw at the injection pump and operate the manual handle of the lift pump until an the
air bubbles are out.
5. Bleed the air from the fuel injector. Loosen the nipple on the fuel injector side, set the throttle to
half and the decompression lever to the decompression position and crank engine. When no
more bubbles appear in the fuel flowing from the end of the injection pipe, re-tighten the nipple.
THIS BULLETIN IS FOR INFORMATION ONLY AND NOT AN AUTHORIZATION FOR REPAIRS
Hope that helps a bit but ALSO check if your hand operated lift pump is actually pumping fuel. There are a lot of problems with these Lift pumps and gaskets. Easiest way to check is to loosen/remove first fitting after the pump (not the exit fitting of the pump) and check for good flow as you pump. If you get little flow or constant bubbles with the flow...you have a leaky gasket and the ENTIRE pump needs to be replaced (about $75) and here's a couple of places to get one from quickly:
If you DON'T have a leak at the pump...
then it is simply a matter of following the piping around and bleeding each fitting until you see no bubbles. Check your hi-pressure fuel pump in the manual as some have TWO bleed screws.
I don't know YOUR engine John so some others may be able to be more specific. Your symptom SOUNDS like a clogged line OR a line getting air into it assuming you don't have any other symptoms like overheating or water in the oil. Rick's suggestion should be checked too!
Good luck on the fix & hope the above is helpful.