Stray vacuum hose?

Dear all,

I have a hose that attaches to the rail leading to the carbs that strangely just won’t stay put, even when I tighten the jubilee clip as much as I can, somehow it works its way off again.

The hose leads to a space in the front wing.

I’ve never noticed any difference to the engine whether it’s on or off.

Does it perform any useful purpose? Is there high air pressure or something in that hose that forces it off? Or maybe I just lack the sufficient elbow grease to get it on properly.

Grateful for any tips.


XJC 4.2 (1976, Canadian spec)


if the inner hose diameter is larger than the metal pipe it is attached to, even torquing down the jubilee clip won’t hold the tube in place. Did you replace the the hose? It looks so new.

Good luck


75 XJ6L 4.2 auto (UK spec)

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Nick - if that goes into the inner wing it is probably connected to the charcoal canister for the Evaporative fuel vapor recovery system (emission control) I’m surprised that you don’t notice any difference in running with that hose off because it connects to the crankcase breather pipe that goes into both carbs. Should create a vacuum leak that would be noticeable - unless maybe the other end is off as well, the carbon canister is missing or broken, or the rubber cap on the breather that the metal pipe attaches to is off or broken. If any of those issues are present as well, putting the hose back on wouldn’t change the way it runs cause you’d always have that same vacuum leak. Oh and IIRC the anti-run-on valve is involved with the carbon canister as well to add another layer of emissions fun.

If you turn the steering wheel like you were turning left you should be able to see the carbon canister in front of the right wheel if it’s there.

The fact that the hose won’t stay on isn’t the biggest issue - I would check all connections to that metal breather pipe to be sure that it is a closed system from the breather at the front of the engine to the 2 carbs.

For testing purposes - once you verify that the metal breather pipe is properly connected to the intact rubber breather cap at the front of the engine and both rubber hoses are connected to the carbs - you can safely block off the outlet on the metal pipe that the loose hose connects to.



I have had this before even with new hoses that won’t grip. I build up a few layers of heat shrink tube to increase the OD on the outlet pipe and refit. No troubles thus far. Paul.

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Thanks all. I have the canister thing. No idea if it does anything. Hose stayed on today. Will check the other connections.

So the hose popped off again despite being tight. I don’t think it’s too big, there wasn’t space for a bit of tape around the metal. So is it possible that pressure builds up and forces it off? I can’t detect anything at idle.

I should have said that another hose leading into the wing and hence I suppose the canister was previously loose and not attached to anything. We decided the canister was redundant so it rid of it.

So assuming the canister serves no purpose now, I guess I should just cap off the pipe and get rid of the hose, but how do I check the integrity of the pipe system running to the Strombergs to know that is the correct conclusion ?

Thanks !


The canister is part of the closed tank ventilation system, Nick, designed to prevent fuel vapor int the atmosphere - part of the emission control regime…

Crudely; vent hoses goes from the top of the tanks to fuel separators in the C-pillars, where a hose from each separator returns liquid fuel to the bottom of the tanks. Another hose goes from each separator, then, joined to a single hose at the rear cage, goes forward through a pressure relief valve to the charcoal canister. A separate hose from the canister then goes to the ‘inlet manifold’ or carb(s) - but the arrangement for this, which intends to suck fuel vapor into the engine while running, is somewhat varying…:slight_smile:

The set-up is sort of complicated and POs have a tendency to be a bit lax about it - not all areas check this part of the emission control system… Having removed the canister; the system is not working anyway - and everything is superfluous…

But(!!) it is extremely important that the tanks are vented - unvented tanks will implode. Essentially, if the vent line from the tanks at the (ex) canister is open to ambient air it’s fair enough, but may cause fuel smells…

xj6 85 Sov Europe (UK/NZ)

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Thank you Frank.
This may explain why my car smells like a refinery. I sense this requires attention but am not sure where to start. I believe that the canister is not connected to anything (or not for long, since the hose keeps popping off).
Your description is helpful, is there a schematic anywhere ? This would help me locate the different parts.

Another thing you might want to check: It is possible that the hose is being wiggled off due to excess engine motion. This could be attributable to a broken or damaged engine mount. Easy enough to check - just rev the engine with the carb linkage while watching it. If the engine moves around (rotates) more than a very small amount that could do it if there is not much slack in that hose. Worth a look.


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Thanks. Yes, I do think it moves excessively when starting cold actually. It settles down when warm but probably still moves too much so I will have this checked.
That’s a relatively simple job right? Just lift the engine slightly in situ and replace the mount(s), correct?

I see that the hose is of the braided type. Hard to get a camp ight enough to grip that slick pipe.

Teh pipe seems tapered. Agin hard to tighten the clamp enough to get a firm grip.

Change it out or plain rubber !

Double clamp it>

This line sees vacum. Not pressure. so, it is not susceptible to being blown off by excess pressure.

YUP a definit surce of gasoline odor.

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Yes - it’s pretty simple. There is a large hockey-puck shaped mount on each side.

Ok thanks. Assuming I get my one hose to stay, any tips on how to get rid of the gasoline smell…? I have the remnants of a second hose emerging from the wing which I guess was part of the set up but we couldn’t work out where it was supposed to go …Haynes manual is short on detail on this point.

There is alot going on with the US Spec S2 emissions system. The anti-run-on valve is also part of this system - probably the other hose you mention. I guess the question is do you live in a place that requires your emission controls to remain intact? If not you can get rid of alot without any real issues but you can’t just start pulling things off willy-nilly.

As for the gasoline smell - as @Frank_Andersen mentioned above, there is a fuel tank venting system that is probably the source of you smell if you don’t have any leaks from the fuel pumps or anything obvious in the trunk floor. Both tank’s vent pipes come into the trunk behind the interior panels, move forward toward the area under the back window, tie together and then go up into a loop in the C-pillar. This loop stops any raw fuel from entering the venting system - only vapor. From there it travels back down into the underside of the car continuing to the vapor canister at the front wheel. The whole system in the trunk has rubber hoses in it that can fail or even pop off if there is a clog in the vent line that continues to the vapor canister at the front wheel. One of my 72’s had a clog in the pipe that ran under the car so it kept popping off a rubber line in the trunk because the tanks have gotta vent. Trunk smelled like a refinery as you describe. If your fuel smell is really bad in the trunk, look at the all the rubber lines up under the rear window area.

There are other possible sources for the gasoline smell of course - you kinda need to localize the stench to figure out what the problem is.

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Right, thanks. I don’t have any real petrol smell in the boot and there is no whoosh from the tanks when I open. But I can smell the car at 20 paces. So I guess the tanks are « well ventilated ». Found a schematic and will investigate further.
Thanks all


What actually happens to engine idle when you block the hose and/or the nipple, Nick? If nothing alters neither end is meaningfully connected to anything - but where things go is still interesting…

Your tanks are likely vented through the detached hose at the canister, Nick - you can try blowing through to the tanks, though tanks are likely venting OK by the smell of it. Mike gave a good physical description of the lay-out, but changes were made to the canister hose connections through the production years - though the basics are still the same…

If the anti run-on system is fitted it’s valve is fitted at the left front wheel well - it applies vacuum to the carb bowls when ign is turned ‘off’ to prevent carbs delivering fuel. You can see the vacuum hoses connected to the carbs…

As an aside; the ‘European’ set-up do not use the emission control system - it just has hoses from the tanks to ground level, instead of taking the venting through the fuel separators.

xj6 85 Sov Europe (UK/NZ)

I have the North American spec with Strombergs and the later type canister in the wheel arch.

Nothing noticeable happens when I take the hose on or off, or block the pipe.

Haynes manual shows three choses at the top of the charcoal canister. It looks as if two of those go through the wing into the engine bay, of which one runs to the metal pipe and the carbs, the other unknown destination. I don’t know about the third, need to have another look, but presumably the petrol tank?

When I next have a chance I will try blowing through the miscreant hose towards the can to see what happens.

I’m assuming that when I achieve the correct set up I should replace the canister.

Out of curiosity then, and forgive my ignorance, how do the European spec cars deal with the petrol smell if they just vent to ground?


Nick XJC 4.2 (1976, Canadian spec)

Normally only two hoses are active, Nick - though the early and later canisters differ…

To summarize; the canister is open to ambient air - there is no vacuum within the canister. With engine running and using petrol; air is drawn from the canister into the tanks via the ‘tank’ line. When the engine is stopped; fumes from the tanks are vented to air through the charcoal in the canister - which adsorbs the petrol fumes, venting only clean air. When the engine again is started, the ‘engine’ hose connected to ‘manifold’ - the engine draws air through the charcoal, drawing the adsorbed petrol into the engine to be burnt…

The third thin hose at the canister’s function is unknown to me - and is only used, for whatever, in the early versions. In short; except for canister differences, the ‘old’ and ‘new’ set-up is identical.

As for the ‘European’ it may be noticeable for the delicately nurtured, but only while standing - it’s lost in the slipstream while driving…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Hi Nick.

One line goes to a ported inlet at the intake manifold, normally via a vacuum valve.

This line vents to the atmosphere inside the engine compartment.

One line comes in from the fuel tanks, normally via a 2psi Rochester valve (engine not running).
This valve has also a vacuum input that opens the valve when there is vacuum (engine running).

All the best.

Dear all,

Ok so I was able to replace the hose with a more supple one and clamp it properly. Staying in place so far. I was also able to take some pictures of the current set up.

The canister has four hoses, see photo. A large, lower one runs to the anti-run on valve mechanism (haven’t tested this thoroughly, engine runs on for a second or so when I cut the ignition). There is a line which disappears into the bodywork which is presumably from the tank, bringing vapour. There is a line which run some through the wing and into the engine bay which is now connected to the carb piping (see photo). And the final line, which also leads to the engine bay and now does not lead anywhere further.

The anti-run device has a line leading to the manifold (see photo).

I’m still a little puzzled. Why run a hose to the engine compartment, fix another hose on the inside, then leave it dangling? This is the one now removed.

I’m also not quite sure why one of the carbs has a nipple capped off while the other one has a hose instead (see picture).

Incidentally, having read some more, i am wondering whether the canister might be choked, per the page in the FAQ, leading to some petrol being dumped on to the floor after a run and hence heavy odours. But I cannot detect any dampness around the canister itself.

Thanks as ever for any further tips!