I think it may be something simple. I think J mentioned trying another gas tank. It may be the connection to the tank. I guess there is a ball valve at that point that may be sticking.
Nailed it on the head. I am guilty of this myself more than once. Chances are when you find the issue you will shake your head and laugh "Can't believe how much time and thought I put into that simple fix 'xyz'!" lmao
I run that in almost every fill up on the boat.... Shit really works good.... And man if you ever decarb that motor it'll smoke like a freight train lol