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    
Crankcase Breathing

Image based on one from the British Leyland Workshop Manual

When the engine is running carb vacuum is applied via the crankcase breather pipe (14) and oil separator (15) to the crankcase and hence the rocker cover, which has a non-vented oil filler cap (16). A restrictor (10) in the rocker cover vent limits how much air can flow to avoid weakening the mixture excessively. Air is drawn through the purge line (9) via the charcoal adsorption cannister (8), running-on control hose (11), anti-runon valve (19) and vent pipe (20) from the atmosphere. As air is drawn through the charcoal cannister previously adsorbed fuel fumes (see Tank Expansion and Carb Expansion) are given up to be burnt in the engine.