The bowl vent on an AMAL
is one of the holes at the back near the air filter
When the float valves fail to stop the flow of fuel it rises till it gets to the vent hole then proceeds to fill the air filter with fuel
Thus when you try to start the bike the air passing into the engine will be saturated with fuel befor the venturri add even more
SO it will be over rich , most likely on the left side as that carb is lower than the right if left on the side stand
IN theory the entire air filter could fill with fuel and then it would run down the carb throat & pour into the cylinder but that would be fairly rare and require a ver restrictive element in the air filter .
So take the filters off and see if they smell of fuel.
If so discard them even after the fuel evaporates the paper will be compromised .