hhmm...
I'm having this problem, or something similar to it...
when its cold if you try and drive it will pop back threw the carb, and will contine to do it if you contine to attempt to drive.. after about 3-4mins its drivable, but is alyways jerky under light throttle and kinda cursing sort if throttle. could very well be two different problems
carb is 32/36 weber and motor is 4ac
replaced a heap of shit a while back, and converted to electronic dizzy, had a huge spark (would arc a strong blue colour prob 4mm or more, with the old points it would struggle to do maybe 1.5-2mm and was a dull orange). but will check it all as i havent since i put the last motor in prob 12months ago lol