If the carb has just been rebuilt, give the rebuilder the benefit of the doubt (no, we didn't do it), that something else may be wrong.
If the engine runs nicely with half choke, then obviously you have a lean condition. That condition could be something in the carburetor, but it could also be a vacuum issue (vacuum leak at a gasket, vacuum advance, etc.). Before re-rebuilding the carb, would at least look at the vacuum.
Jon.
