I know this conversation is really old but I’ve been experiencing the same problem as everyone’s described. I’m not very mechanical savvy or experienced so I’m going to explain this by what I know lol. I realized the click or pop sound was coming from the part on the bottom of the carburetor that a wire connects into. When I pulled the carb and intake off originally to diagnose it with starting fluid into engine I realized that the carburetor was completely flooded with gasoline. I pulled the fuel line of the carb and realized that even when the acceleration/speed increase was all the way pulled down to the bottom, it constantly let fuel flow from the tank into the carburetor. The engine would crank but not start because of the carb being completely flooded out. I’m not positive how or why but I’m assuming the carb being flooded trips the sensor that’s plugged into the bottom of it and that causes the battery to drain while the mower is sitting. Somebody mentioned above about adding a fuel shut off valve and that’s exactly what I’m going to do instead of disconnecting the fuel line from the carb when finished mowing. Hope this helps!