Post #2 had the most likely answer as to why you keep getting a hydraulic lock. If you use the muffler pressure line as the vent when filling you can overlook that the tank is full and it's trying to fill up the muffler. Getting an inverted engine to flood by priming with a finger over the carb is much harder to do because fuel then has to run uphill first before it can even get into the engine. After you figure out how to get fuel to run uphill then you have to be sure not to overprime.