I had the same problem.The solution is you need to clean the carburator.Even though you probably took all the gas out before storage.There was a drain hose with a plug that is connected to lower part of the carburator that still had gas in it .If you didn't empty that gas .The gas fouls the carburator.I cleaned mine myself.I took out the storage compartment that is under the seat and cleaned the carburator and jets .Here is a video on how you can clean the carburator
YouTube - STOCK 50CC SCOOTER CARB CLEANING #2