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Remove the gas cap to take the possibility of a plugged vent out of the equation.

Is there a modern inline fuel filter installed? Remove it if you do.

Does the gas line flow down hill all the way to the carburetor? I've found A's don't like having the gas run up hill at any point in the fuel line. Not sure why but it seems to make a difference.

Check to make sure your fuel line into the carburetor isn't protruding too far and is pushed up against the fuel filter in the carburetor.

Check your firewall mounted fuel filter to make sure it is clean.

Do you have a pencil filter in the tank? Blow some compressed air into the fuel line to clear any debris that may be blocking it.

I know you said you had strong fuel flow but checking all of the above won't hurt.