Gas is leaking out the back of the accelerator pump and down the outside of the carburetor.
The pump stem you see on the back of the carburetor is part of the accelerator pump diaphragm and any gas leaking out here means the accelerator pump is leaking. Rebuild, or at least replace the pump.
When accelerating there is a gap between idle & cruise and extra gas is needed to get over this gap. That is where the accelerator pump circuit comes in.
The pump well is fed via the pump inlet check ball which resides in the economizer block. When stepping on the gas, the pressure of the fuel will close the inlet check ball and lifts up the pump discharge check ball.
If you are getting too much fuel at idle, the pump discharge may be leaking. With the engine at idle, look down the carburetor and see if gas is seeping out of the pump shooter.
