Stalling Issue 86 Nautique

My 1986 Ski Nautique w/351 PCM is currently having stalling issues. It runs and idles fine for about an hour. It will just shut down for no reason at slow speeds (1,000 RPM's or less). If I get it above 1,000 RPM's it runs great. Again, I get about one hours use out of it before it acts up. I can start it right back up after it stalls and rev it up. The engine had only 570 hours. New fuel filter installed today, new impeller (it's not over heating), fresh gas, new plugs and wires. Any suggestions? The key is that after an hours worth of use it's like somebody hits a switch and it shuts down.

Thanks,

Ken Spurling
Upton, Massachusetts

Not sure about the ignition coil. I believe that it is in the electical system (ie bad condensor, points). There are signs that the points are "flashing". It stalls like somebody just turned the ignition off while underway. It's not the rough and rumbly fuel / carburetor feel. It's also not the vapor lock feeling either.