There was a time that all cars vented to the atmoaphere. No seense of petrol odor as I recall.Air with fuel particles probbly heavier than air, settled to groud. Aaway from human nostrils.
My theroy!
Carlt
**
Over time, the charcoal loses its adsorption quality and may solidify, Nick - which is why changing canister/charcoal is a scheduled maintenance item…
At least two different canisters were used - with different internal hose passages - however the principle is always the same; the charcoal divides the canister into two parts. The hose from the tanks enters at one side, the other side is vented to open air - petrol fumes from the tanks sticks to the surface of the charcoal, is ‘adsorbed’, without entering the atmosphere. With the engine running, the hose to the ‘manifold’ draws air from the atmosphere through the charcoal - and draws off the adsorbed petrol fumes, to be burnt in the engine.
Strictly speaking, only three connections are required; open air, to tanks and to the ‘manifold’ - exactly how this is done on variations of canister I do not know - only the simpler, later type. Two points are essential; the connection to the ‘manifold’ should be ‘strangled’ to reduce air flow/vacuum - directly connected to the manifold/carb vacuum is not intended. Secondly; if liquid petrol enters the charcoal, it is absorbed into the charcoal, saturating it - this ruins the charcoals adsorbent properties and will contribute to it solidifying. It will also allow petrol fumes escaping to the atmosphere - negating the intent of the closed tank venting system. And if the charcoal blocks air flow; vacuum is applied to the tanks - with ‘unfortunate’ results…
The adding of the anti run-on valve to the equation complicates matters in as far as it is connected to the canister, but basically lets ambient air into the canister. The reason for fitting the anti run-on is simple; as ignition is turned ‘off’ and the engine is still spinning down, vacuum is still present the manifold. And as long as there is manifold vacuum, the carbs will deliver fuel - which may be ignited by ‘glowing embers’ in the cylinders, and the engine runs on. Erratically and for some time…
With the anti -run on fitted; when ignition is turned ‘off’, a special connection in the ign switch applies power - via an oil pressure switch which is closed while the engine is turning/having oil pressure - to the valve. Which closes off ambient air, and opens the hose connections between valve and carb bowls to manifold vacuum. With manifold vacuum in the carb bowls, the carbs cannot deliver fuel to the manifold - and without fuel to the manifold the engine cannot run.
So the connection to the anti run-on valve normally provides ambient air to the canister (and carb bowls) - but I cannot help you with the hoses’ connection within the canister. Nominally, the canister cannot be dismantled for inspection or changing the charcoal - but it has been done DIY, using charcoal normally furnished for aquariums.
You have to use your own judgement for further investigations, but clamping the hose from canister to ‘manifold’ should cause no, or only tiny, change to idle rpms if the ‘strangler’ is present. Blowing through the ‘tank’ connection should elicit some sound at the tanks.
Carbs are sometimes fitted with two nipples for ignition/dist vacuum; one giving manifold vacuum used on ‘European’, the other giving ‘ported’ vacuum used in ‘US’ set-up - the unused one being capped off. ‘Ported’ vacuum is ‘0’ with throttle closed - in idle…
Frank
xj6 85 Sov Europe (UK/NZ)
Being a North American spec '76 you have literally every pollution control system that Jag had to install pre-fuel injection. Those fittings on top of the carbs may be EGR (exhaust gas recirculation). Earlier cars had a fixed orifice system - literally a simple tube from the exhaust manifold to the carbs - IIRC your car has a more complicated system.
Some British Leyland cars from that era had a distributor with both vacuum advance and retard together - your car has retard at least… If your distributor vacuum capsule has 2 vacuum nipples it has both and the fitting on top of the carb is the advance half of the equation. They only used one carb to control the dizzy vacuum so that could explain the capped off fitting on the other carb.
As I mentioned before, there is ALOT going on with the pollution controls on these pre-injection S2’s…
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Thank you everyone. Since I clamped that hose properly, there is less fuel smell. Not zero, but less. That leaves one still open but I think I will leave it at that for now …