You did a good test: When the engine starts to crap out, have a buddy constantly prime the fuel hose bulb. If the engine picks back up and runs great at WOT- as long as you constantly prime the fuel hose bulb-likely you've got a fuel supply problem. That could be: weak/damaged fuel pump, bad fuel hose, dirt in the anti-siphon valve, etc. Does this have the original VRO (OMS) factory pump still on the engine? The fuel hose should pump up hard first thing each day. As the engine draws fuel through it, the bulb will get softer, but should not collapse. That's normal. It should pump back up firm-each time you re-prime the bulb. With age, the ball valves in the hose bulb may not work properly. If you notice, the hose bulb should be generally oriented with the arrow pointing slightly uphill/skyward. They can cause problems if they lay in a downhill orientation in the boat's splashwell.
