I was initially concerned with fuel delivery but have ruled it out. The gas tank had horrible varnish which I thoroughly cleand. I replaced the petcock.....twice. I replaced with the original carb with miniky clone (I didn't even bother with the original carb because of the varnish situation and couldn't find a complete rebuild kit at the time). In fact, I tried two different miniky VM12 clones. I've tried various inline fuel filters. I've even cut the screen off the petcock since I was using an inline filter.
My initial suspicion of fuel delivery was because the motor would stop after 3-5 minutes and when I would look down at the clear fuel line I could see a gigantic air bubble move up the line. Then the motor would start after 30-60 seconds, but only for a brief run (less than a minute). One time when it died i shut the petcock off and actually clamped the line above the carb. The float bowl was full of fuel....so I ruled out fuel starvation. FYI - I checked the float height by using eyeballing the clear drain line next to the bowl (while drain was open). Furthermore, had the same results with two clone carbs.