I've ran pressures from 7 down to 4.5 while running the engine. It didn't make a change in performance. I have not looked down the carb when it starts to chug or pop out the exhaust. I did change carbs to one from a.running car with no change. I can say there is a lot of unburned fuel.
I’d run it to warm the engine up a little then turn off the pump and then bring up the revs to (where you had the chugging) and see what it does, before the bowls empty.
