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/Contraction     Carb Expansion     Crankcase Breathing     Anti-runon    

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 canister (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.

In 1978 a second charcoal canister was added below the anti-runon valve (19), to the air vent pipe (20). As the valve was connected to the inlet manifold fumes there could escape to atmosphere via the valve. The second canister trapped these, and was purged in series with the main canister during normal running.