If the problem started right after installing a rebuilt carb; do you have the old carb which you can reinstall to see if the problem goes away?
If the engine runs on one, but not the other; you have the answer.
If you no longer have the other, then the suggestions concerning vacuum leak checking are good.
A good rule of thumb (in the absense of other knowledge) is (1) compression test; (2) check for vacuum leaks; (3) check the ignition system; (4) check the fuel delivery system; (5) check the carburetor.
In your case, if the engine ran fairly well prior to changing to this carb, I would probably suspect the carb is defective.
Jon.
