[Chesfisherman1]

I just spent 3 days on a similar fuel issue.
I have merc 7.4L inboards where I converted the water/fuel systems from single mechanical water.fuel pump to electric fuel pumps and camshaft driven water.

If you go from the tank to the carb my configuration for both engines is as follows:
-shut off valve
-antisphion valve
-hose from top of tank to engine room
-water/fuel filter
-electric fuel pump
-combination of hose and metal hose
-carb

now for my issue-
-one of my electric fuel pumps was not building pressure to the carb. You can hear a variation in fuel pump clicking when it is dry running vs wet and building pressure (low pressure).
-I changed electric fuel pumps-not the answer
-I remove antisiphon value-not the answer
-I configured both engines to work off of working fuel line and electric pump-Worked
-I configured both fuel pumps into the non-working line-----LEAK LEAK LEAK
-the leak was located on the inlet to the electric fuel pump that had a barb hose fitting that was over tighten by me during my debugging.
-the barb fitting was also a single barb which is prone to error (over/under tightening).

My fix-new hose-new/sea clamps/correct position of sea clamps on barb to ensure proper seal,
(also order NTP to flange fittings for all fuel connections-they are idiot proof-which I appear to need).

So given your engine starts but after shut off will not restart you may not to be getting proper fuel pressure into your carb.
Is there a variation in the tone of your electric fuel pump before and after this condition?
Do you know the oil pressure trigger pressure/go-nogo level for your system? (mine installed by oil pressure sender/in area of remote oil filter).

Please BE VERY VERY CAREFUL DEBUGGING FUEL SYSTEMS---BATTS OFF MAIN SWITCH BOTH ENGINES---BATT CHARGER OFF---NO SPARK POSSIBILITY IN ENGINE ROOM---NO SMOKING---DURING ITERATIONS---BLOWER BLOWER---VISUAL INSPECTION WITH FLASHLIGHT---

Hope you get it fixed.
Best,
Chesfisherman1

at start but it is not maintaining proper pressure to maintain stable running.