North American Emissions Plumbing - Twin SUs with 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     Anti-runon    
Carb Expansion

Image based on one from the British Leyland Workshop Manual

Any expansion and contraction of fuel or air in the carb float chamber moves through the vapour pipe (5), charcoal adsorption cannister (8), running-on control hose (11), anti-runon valve (19) and the vent pipe (20) to/from the atmosphere. Petrol fumes from the vapours are adsorbed by the charcoal and not discharged to the atmosphere. If the engine is running any fumes from expansion are drawn into the engine and burnt, see Crankcase Breathing.