Nice summation guys :thumb:
I think the internal (closed side) flow rate has yet to be determined. At one point I had looked to see if I could find some relatively inexpensive flow rate indicators . . . sort of like a visual pinwheel indicator . . . to get a visual on the open side water flow. I didn't really find anything that was right sized for the application . . . unless I wanted to spend a bit of green.
If I can find something, then maybe I could also monitor the closed side flow rate as well.
I did at one point disconnect the open side hose that leads to the exhaust elbows to get a quick visual on the flow of raw water from the HE. Looked fine. . .
One thing that I did along the way was to run a very intense (50/50 mix) of injector cleaner and fuel through the port engine. That may have given the injectors a bit of new life, re-gaining some of their efficiency, and perhaps making the fuel mixture a bit richer.
The only significant clues so far have been the lean burn looking spark plugs (which now seem to be fine

) and the lower pressure at the fuel rail. Yet to be determined is if the recirculating pump has some issues.
We will be using the boat this weekend and then not for a couple of weeks, as we will be vacationing in the Western USA - Grand Canyon, Yosemite, Arches, etc. I should have the parts by then (seem to be special order since they were used only for 1-2 years back in the 1996-97 time frame). So, probably not until the end of August will I have an update.
Game plan would be:
Replace fuel pressure regulator
Remove/inspect recirc. pump.