By any chance were any of the parts sandblasted near the fuel tank..? Hood, etc..?? Did you take the inlet strainer out, and check it..?? I'd also check the atomizer nozzles, and see if there may be something plugging those itty bitty holes. Does partial choke make a difference..??
Taking out the drain plug in the botom of the carb, should assure you you are getting plenty of fuel past the float needle valve, and the float not sticking.
If a spec of sand in plugging a port, all the soaking in the world will not make a difference.
Was the manifold removed? Maybe a intake gasket leak there..??
I have heard them run a little rough when the throttle shaft bushing was worn, and allow extra air in, but smoothed out under a pull.
Guess it depends on how thorough of a restoration was done. Cleaned, prepped and painted, or complete overhaul included. Could be some cleaning unsealed something, that was covered with gunk, and allowing too much air in.