That is not only frustrating but loosing thrust at a critical moment can be dangerous.
Please provide some more info: did this symptom only occur after the carb rebuild or was it the reason to rebuild the carb? Does it idle at all or does it only stall when coming off throttle? How do you get it started and into gear? If will not idle at all, what is the minimum RPM needed to keep it running? Did you do the carb rebuild? If yes, are you 100% confident that all the passages are free of debris?
The idea here is to provide as much info as possible to help the good folks here diagnose or provide steps for you to try and report on to get this resolved. Thanks.