a carburetor outer vent control device for use in a fuel system of a motor vehicle of the type including an outer vent provided in a float chamber of the carburetor , a charcoal canister and a fuel vapor line coupling the outer vent with the charcoal canister . the carburetor outer vent control device includes a valve means provided in the fuel vapor line which is only open when an excessive amount of fuel vapor is present in the float chamber and an engine of the motor vehicle is not running .