I'd guess that one of the lines has a pinhole in it that's preventing fuel flow, or that the tank is sitting way below the spray bar in the carb. Does the tank have a clunk line inside? Is it kinked?

How sure are you of the needle valve setting(s)? Try turning the high speed needle all the way in (don't tighten it, just until it stops!) then back it out about 2 to 2 1/2 times.

Try the needle valve setting first, then replace all the fuel lines, including the one in the tank. Maybe replace the tank too.

Let us know how it goes.

Good luck and welcome to RCU!
Dennis-