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.