manual choke or automatic?

did you rebuild or someone else on the carb?

I can't tell what kind, but if it is the holley type, my first time I rebuilt one, I used the wrong gasket set. it wouldn't idle.

could be the gasket under it, could be a hose you can't see the crack in.

So lets do a little diagnostic.
if you have a helper, hold the choke closed, see if it will start with your foot on the floor.

next, try pumping the gas say 5 times first, if it is warm. see if it will catch and then die when it runs out of fuel.

you can try it with 10 pumps as well. leaving the choke open.

if it starts and runs like that, I might agree, a vacuum leak somewhere to start looking for.

if it doesn't, then I would check the carb again to see if it was rebuilt correctly.