Your problem is the tank most likely because on all tanks you should get fuel just coming out the fuel line when the petrol cap is secured. All you need to do is close off the return line and see if fuel comes out the pickup line.
Note that the carby will not suck fuel when dry and that is what happens when you don't get fuel coming up the line. The tank should build up pressure to push the fuel up the line and I notice in the picture the tank has been damaged at some time.
I would be replacing the tank first then look at the carby. It appears you have put the cart before the horse and that really does not work.
