The Saga continues. We rebuilt the carb. It worked for a few days, then it started stalling again. No amount of tuning would fix it. So we bought a remanufactured carb and tuned that. Still stalling.
I started suspecting it wasn't the carb at this point.
I was going through every vacuum test I could think of when it did this on the exhaust restriction test:
https://youtu.be/Z_I_cT5yRos
Is it possible this has been an exhaust restriction the whole time?