Fuel issues

Hey all quick post here.
I recently put a new fuel tank in my 69 valiant and have created an issue somewhere.
If I leave the car for more than a day, the fuel drains down to the point where I have to crank it for a good while in order to bring fuel back up to the carb. I thought maybe there could be an air leak somewhere allowing the pressure back down. But all the possible areas seem to be OK. HMMMM lil help here? thx Donnie