My brother and I kicked ourselves in the butt over the fuel tank - we did a lot of things, like replacing the fuel pump, before figuring out it was a nasty tank. The sad part is we had a good sign the tank needed at least checking when we had to replace the sending unit because the float was 1/3 (if not more) rusted away causing the fuel gauge not to work.
Hind sight is sooo 20/20
on my thread from last year. After reading it over again we were also fighting a bad carb I got off eBay - which is one of the main reason when I finally got what I think is is good replacement I sent it off to Quadjet Power. Everything I have read is nothing beats a properly turned Qjet!
You very well may be dealing with a Carb that needs to be rebuilt but insuring your tank is in good shape, IMO, is a good thing to check out and to eliminate as an issue.