Hover over a number for the key, click on the menu items below to show the vapour/vacuum routings.
Fuel Flow Tank Expansion/Contraction Carb Expansion Crankcase Breathing
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.