Disclaimer first... I'm not a mechanic. Did you have the problem before the new carb, electronic ignition, racor, etc? Do you have a fuel tank solenoid valve? If yes, it may not be functioning properly or was inadvertently disconnected. If no, that might help -- I'm certain someone else will chime in either refuting or confirming my hunch
My A4 has a fuel tank solenoid valve that acts as a fuel shut-off. Just an educated guess.