I suspect that the float valve is not sealing allowing overfilling of the carb. When you turn off the key it is killing the fuel solenoid on the carb preventing extra fuel from being drawn into the main jet of the carb. or the main jets fell out when you took the carb apart.
item 117 or 117a in this diagram
https://www.partstree.com/models/44...-engine/carburetor-kit-carburetor-overhaul-3/