If it runs great accept for the idle the choke is a unlikely cause. The needle is more likely, but I think he would have thought of that having done so much jet work.
Having to run a #80 jet on a nt is unusually rich. Did it idle very high when it was jetted at around #70? I could be off on this, but my thinking is a small air leak could be corrected with jetting explaining the need for a #80. If the leak were in the intake and corrected through jetting it would most likely run good through it's entire range, but if it were at the crank seal at higher rpm it may run fine while at low rpm case pressure may not be high enough to deliver a good charge and die.
So the needle height if not yet addressed is the starting place. Move the clip all the way to the top and see if this helps.
I still think their is a problem some where causing the need for a #80, but if I'm wrong you might want to run a little hotter plug NGK b6hs
It wouldn't hurt to look for a possible intake leak and a look at the crank seals, especially the one behind the rotor to see if it's pushed out a little. They should be flush to the case.