Fuel feed air lock

rusty_apache

My 29 Essex fuel feed canister gravity flows perfectly but if I allow the fuel feed to empty, entirely down to the glass sediment bowl it develops an air bubble in the small chamber just above it, no amount of fuel in the canister will push out the air bubble and fuel does not gravity flow into the carburetor.

When I shake the car from side to side it is very clear that the bubble moves but will not burp up into the next chamber. I have double checked the spring loaded conical shutoff stopper and it is not preventing the fuel from flowing in or air from escaping upwards.

What am I missing here?