Hydrolocking as was explained is basically in a model engine filling the combustion chamber with fuel causing it to lock up. The most common cause of this is the fuel tank being higher than the carburator. Ideally you put the fuel tank at the same level as the carb so no fuel will gravity feed into the carb. If this isn't possible then there are other ways such as a Kline fuel regulator or turning the engine over backwards at first so the fuel gets pushed out of the cylinder up through the carb clearing it out. Then starting it normally.

Randy