Carburetor

I have a 69 coupe deville and I ran it on empty for
the first time and put gas in it and it started running
terrible. The car felt like the tranny went out or the
gas was extra bad. It barely made it home and it
was only going maybe 10 or 15 mph at the time
while I'm flooring it. My needle valve on my
carburetor was down so I took it and got it cleaned,
because it had already been rebuilt. After that I put
the carburetor back on and cranked the car and it
ran but still sounding and running horrible. I never
tried driving it after that but I'm curious to what I
should do next or to look for... I know I need a new
tank, but while the car is running you can just hear
air sucking from the carburetor what's making it do
that?