Rob, I am surprised to see a man of your stature on the Brickboard stumped. With the symptoms you described and if it were a 740 I would say bad Hall sensor or it's connector, but not the case here unless something fishy in the 240's dizzy. But that would be unusual.

If you had a no start situation it would be much easier to troubleshoot. Intermittent stalling with immediate restart can be tough. I think power stage is a prime suspect here. What about ignition switch?

I have always believed in answering that ultimate question (you know the one about spark or fuel) by carefully observing the tach. You may know tach pulses are fed right off the coil negative.

Therefore:
Engine cuts out at speed, tach jerks down immediatley and rapidly to 0 even before the engine winds down means you have lost spark.

Engine cuts out at speed and tach continues to track engine rpm as engine winds down means fuel problem.

Tach can even be observed while cranking during a no start. The ignition pulses at coil are reflected at the tach with very slight needle movements.

Of course all of the above assumes that rotor, cap, wires and plugs are all good.

What about gently jiggling various wiring connectors and harness sections to see if you can induce a stall during idle.

Just my thoughts. Good luck, be sure to post progress and results.

--
David Hunter