Hover over a number for the key, click on the menu items below to show the vapour/vacuum routings.

Note that as the float chambers fill air is pushed out through the canister, and if there is a problem with float or valve and the float chamber overflows then fuel will be pushed this way as well.

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.