After running out of gas the van will not start

This van has always started! It has duel tanks. I was driving the van and it ran out of gas. I put five gallons in each tank. Now, I cannot get gas to the carburetor. It fires right up and runs for a few seconds when I use starter fluid or gas directly in the carburetor. Is there a filter along the gas line? The tank switch (on the frame) clicks when I change from front to rear. The mechanical fuel pump is new, as is the filter on the two barrel carburetor. What could this problem be? Thank you!