OK, time for plan B I think.
Swapped it out for a new Dellorto 15.15 with a 60 jet. New muffler has basically no carbon build up. All carb seals good and tight. And same thing happening, only starts if I pedal the heck out of it and dies below half throttle. I have other jets but I think 60 should be close enough to tell if the carb was the problem which it doesn’t seem to be.
Could it be the timing is off a bit? The points are clean and gap is correct. Any other ideas?