Just a wild guess - or something to think aout.
A boat pulled into our marina, engine stalling, started up moved a few yards, engine stalling, started up moved a few yards and eventually, it died totally and we pulled it onto the the 'pump-out / Fuel pontoon.
Went thru everything 'simple' fuel pump working, fuel filter ok etc etc - owner said not a problem with fuel levels as he had dipped it and there was about 8 or 9 inches of fuel.
Long story short - seems that there was enough fuel getting pumped thru' to run on tickover for a few seconds, but as soon as put into gear and any throttle appled it died, when the boat moved the fuel sloshed-about and pumped just enough to start it again.
Fuel pump was "Out of Order", so gave him 20 litrs out of my Jerrycans, engine started, did a few laps of the marina under power and was a happy-chappy.
Moral of the story - check your fuel level is actually higher than the pick-up-pipe.