Leaving for a short cruise last Friday, I fired the engines up about 1/2 hr before planned departure. After 5-10 minutes, I walked to the stern to check water flow. Both sides OK, but as I was looking at the port tube, the engine coughed, then quit. Cranked engine, no start. Pulled top off Racor, can half empty (or half full, depending on your outlook on life). Filter looked clean, changed it just because, filled can, primed with manual pump, good flow out of injector pump bleed. Tried to start, cranked for 5 seconds, nothing. Cranked again, advanced throttle quickly to full, fired up, idled smooth. Ran 10 minutes or so, coughed and died. Checked Racor, half empty. Just because it’s easy to do, switched port supply and return over to keel tank. Filled Racor, etc, cranked 5 sec, no start. Cranked and advanced throttle, fired up, ran smooth. Half hour later, still running. Decided to proceed with weekend anchor-out, ran 2 hrs to destination, no issues. On Sunday afternoon, stbd engine started right up, port cranked, no start. Cranked again, advanced throttle, started up, ran smooth, ran about 3 hrs to home with no incident. I’m thinking I have an air leak somewhere between the main tank port side pick-up and the manifold valve, and have no explanation for the new need to advance the throttle to start. First thing I’ll check is the pick-up tube, although I don’t think that’s the problem. I think all the line between the tank and manifold is copper (to be confirmed), so the manifold valve itself might be the most likely culprit. I’ll report back after inspecting the pick-up tube, piping and manifold valve. Meantime, any suggestions or ideas are welcome. TIA