North American Emissions Plumbing - Twin SUs without Anti-Runon Valve
Hover over a number for the key, click on the menu items below to show the vapour/vacuum routings.
Fuel Flow     Tank Expansion     Carb Expansion     Crankcase Breathing    
Carb Expansion

Image from the British Leyland Workshop Manual

Any expansion and contraction of fuel or air in the carb float chambers moves through the vapour line (5), the charcoal adsorption cylinder (8) and the vent pipe (11) to/from open air. Petrol fumes from the vapours are adsorbed by the charcoal and not discharged to the atmosphere.