well you definitely gave me somewhere unique to look! I did have quite a bit of pressure in the fuel line when I disconnected it before I rebuilt the carb. I just redid the gas tank (pulled it, pool acid wash) and I know the vent line is free and clear. I'll look for black smoke too...my gut still tells me it's trying to run too rich or somethin. Right now it's 2 turns out both sides.
Before I rebuilt the carb I remember now that when it did this I messed w/the idle screws and it settled down- when I had them about 3.5 turns out each. Then when I went to start it again it did the same thing later.