There are several things that could be causing your problem. First, make sure all vacuum lines are snug on their fittings and are not cracked or split. Also, make sure there are no vacuum leaks at the intake manifold-to-cylinder head gasket and the carb-to-intake manifold gasket. Next, make sure the idle mixture screw on the carb is properly adjusted. After that, make sure the oil in the carb damper (the screw cap on top of the carb) is the correct type and at the correct level. Oil which is too heavy will cause stalling. Finally, the idle jet in the carb could be clogged. This will require taking the carb apart and blowing out the jet and passages with compressed air.
Also, if your mechanic rebuilt the carb and it isn't functioning properly, he should be more than happy to correct the problem, not act chagrined that you brought it to his attention. Tell him you expect it to be fixed properly or you want your money refunded. If he refuses, or is unreasonable, take him to court and/or find another mechanic.