1973 Mercury 650 Stall problem. HELP

This motor has an electronic ignition and starts and runs great with one exception. When I put the boat in the water it starts on the first turn, Idles fine, but when I take off across the lake, after a couple of miles with the motor about full throttle, it will simply die. There is no sputter, its like someone flipped a switch and shut it off. Sometimes as the boat is slowing the motor will start up again by itself but not always. However it always starts right back up when i turn it over. In the afternoons, after trolling all day the problem goes away and the boat runs perfect back across the lake. Help, What would make this happen. The gas vents are open, the rubber pump hard, but I can't tell if its fuel or electrical. It just doesn't make sense

Re: 1973 Mercury 650 Stall problem. HELP

Even though your problem sounds like fuel, it could be a high speed (blue) coil in the driver ignition system or a bad connection on the wire to terminal board (block) in the driver--Bob

Re: 1973 Mercury 650 Stall problem. HELP

I had the same problem with my 1973 650. What I discoverd was that the fuel line where it connects to the motor was sucking air around the seal. A new gas line fixed the problem. I hope your fix is that simple.