[TheBearAK]

Bad primer can leak through, pinch off the line going to or from the primer and see if it stops.

Another possibility is fuel pump diaphragm is leaking back through the pulse line and into the carb.

 

[TheBearAK]

Fuel can only dump out of the carb if the supply is not being stopped. So what stops the supply? Needle and Seat. These components are under the float hinge and operated by gravity and the float. If the needle doesn't seal up inside the seat, fuel will leak past it and then either out the front of the carb or into the engine.

Into the engine can damage the engine because while rings are a decent seal, they will still allow gas to seep down around them and into the crank case.