That's the float bowl vent. Your carb is probably gummed up so the
float won't raise up to stop fuel from entering the bowl.
Therefore it will overfill and spit out the vent.
Or the float itself is bad and the same thing would happen.
Especially if it hasn't run for a year, I would say it's gummed up.
Take it off , clean it out, put a few new gaskets on it, mabey some
new float adjusters and your good to go.