Mark, I've had these symptoms before. It was a loose rpm sensor with wire caught up in the transmission dipstick ( as left by a 1/2s mechanic, reason 22 why I do my own work) causing intermittant start problems just like that. In yours, the hall sensor on the distributer apparently takes care of this function. Heed Bills advice and look for the rpm needle to move during cranking when youve got the no start. You might unplug the hall sensor and confirm a no start for that condition. Also notice it during the start so you'll know what it looks like. When was the last time you had the fuel filter changed. Its easy to ignore and will ruin your fuel pump so its a good thing to do anyway. Scroll down and look at my post of this weekends problems. BTW, if you check ignition with a timing light, it may not fire from normal cranking but should fire at idle rpm, so watch for false negatives. You could use a spark tester or make one from nails and set the gap at 3/8 to confirm that your intermittent problem is not a spark problem. another way to test spark would be to pull a plug and jumper the threads to ground and check that the plug fires at crank. Keep safety in mind as fuel will blow out the open plug hole and spark plug voltage can kill. Spark testers completely bypass he plugs. For now you can pull the plugs during no start and see if they are wet. My problem this weekend was an ignition problem that I thought was a fuel problem. In retrospect, 3 of 4 plugs was wet. The dry one turned out to be the only cylinder that was occasionally firing. Another was to verify a fuel problem is to put some fuel in the pistons when you close it up and see if you get a goose out of it. At least one cylinder should be ready to compress and fire but I havnt done this on 4 strokes, only 2 strokes( fire every time at tdc). You could also inject some fuel into the throttle body like I did in my post and see if the engine gooses on crank because of it. Remember safety and do this only on a cool /not run engine. Above all, I'm just a hack at this, so take it with a grain of salt.