Carbon canister removed issue

This one is for all those that have removed the carbon canister…

So, I did that (carbon canister removal) during my long project to fix a bunch of stuff. Part of the reason for that was my suspicion that the return vent hardline was clogging and not allowing the gas tank to vent properly. I used to get lots of whooshes when opening the gas cap. I disconnected the return hose from the hardline back to the carbon canister and put a lawn mower fuel filter on the hose, mainly for the hell of it and partly because my OCD was telling me that if some situation happened I could end up with stuff getting sucked into the tank.

In any case, was heading to a car show for my first drive more than block and filled up with gas. Was gonna try and stop early, but it filled it till the thing clicked off. As I was driving off, a bunch of gas was coming out through that return hose. And then after about 2 quarts came out, it stopped.

I’m wondering if other carbon canister removal owners have experienced that and what the solution might be. Maybe this was a one time thing, filling up the tank from almost empty to full. Don’t know just planning for the next fill up.

I finished 3rd behind 2 e-types, got to drive the car for about 50 miles, and had a blast, so not too worried, but OCD is starting to kick in again for a fix :slight_smile:

Now, pretty pictures…

^^^ That’s the return hose with the fuel filter on it that poured out some gas after a full fill-up

^^^ That’s the XJS from the front with the competition behind

^^^ Those are the 2 e-type winners with my XJS butt sticking out at the end…

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that seems strange could it also have happened with the canister hooked up…so how did you know gas was coming out… where exactly is that new filter located… can’t tell from your picture…

Fuel never spilled on the ground before. I knew it was spilling out because you could see it. And after about a quart of gas spilled out it stopped.

So let’s see, here’s the order of events:

  1. Most gas removed from main tank and sump
  2. Hose disconnected from hardline that runs from tank to canister and added lawn mower filter to hose
  3. Added about 5 gallons of gas to test car
  4. Drove car around to test
  5. Drove car to Shell station to fill-up
  6. Added gas till the pump handle popped, probably around 17 or 18 gallons
  7. Headed out of the gas station I hear my son yell at me from the trailer car that something was leaking.
  8. Turned the car around and parked out the station
  9. Shut the car off
  10. It was quite clear where the gas was coming from and you could follow the gas trail, but it was just dripping when I was under the car
  11. Fired her up again, drove back to the house to pickup a plug just in case it started leaking again
  12. Hasn’t leaked since and no whooshing anymore when popping the gas cap

Key things might be the fact that it was noticable when the car was running. Not to say it wasn’t leaking after fillup, it just wasn’t noticed till driving.

Could be that the hardline is clogged, never allowing fuel to overflow to the canister, but since I’ve had this car since day one it’s never spilt fuel. Or it could be that the whole canister system provides enough back pressure to prevent overflow into the canister.

Now that she’s running again, I’m eating gas so we’ll see what happens next fillup when I’m expecting a potential problem.

Ok, annotated pics…

^^^ That’s that hose connected to the hardline behind the rear b bank side

^^^ Lawn mower filter on hose

Looking at the Parts Catalogue, maybe it has to do with the pressure/vacuum valve (CBC6280), since that piece is no longer in play?

Nah. I’m not buying that.

Something is pressurizing your fuel tank if you’re getting fuel in that line. It’s there solely to collect vapors. It collects those vapors from the top of the tank.

Perhaps a few drops would come out when you topped off at a gas station, but certainly not quarts!

I guess to check that theory, next time you top off, do not replace the fuel cap. Drive and see if there’s any fuel leaking out if you drive without the cap on.

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HI, I was reading with interest about the carbon canister. I too have removed all the unnecessary vacuum plumbing which included the charcoal canister. I connected the tank vent hose directly to one of the B Bank inlet manifold tits. I have run the car in the garage and all good at the moment but was wondering if this will cause a problem when running at higher revs and wether or not it would suck in raw fuel after filling tank. I thought I had this sussed but after reading the above and giving it more thought, maybe I have a potential problem looming. love your thoughts. Thanks

Unless you turn the car upside down I don’t think you will have a problem.
If the fuel caps are hermetically sealed there will be no flow, just vacuum.
And on higher revs the vacuum is almost zero.

The thing I don’t know though is if at idle the 18inHg / 9PSI vacuum is high enough to collapse the tanks.
Another thing is when the car sits for a long time fuel vapours may accumulate and condense inside the intake manifold.

Very good points you make. when the line was attached to the charcoal canister, it vented all vapours gathered across the engine and fed them into the manifold anyway, so Im not sure that what I have done is much different than normal fit. I take your point re condensed vapours sitting in the manifold. Our climate in Australia is generally warm and was wondering if it sat there for a time that the raw fuel would evaporate anyway??? Not sure. Q. Would what I have done be much different to scavenging via the canister???

Basic thought- If you are going to remove the Carbon Can anyway- why not plug that line and vent your cap? Mahe it all dead reliable and “Pre .72” (+_). ?? A whole would do, or a vintage cap.

So the gas tank is supposed to be vented while running, not sucked out. The line to the top of throttle body (or pcv line on some cars) is to remove the charcoal canister fumes. The charcoal canister has a vent hole in it, that is where the tank ventilation comes from.

When the car sits, that’s when fumes can build up in the tank. A valve keeps that closed, unless it builds up pressure above (1psi?). If so, those fumes are sent to charcoal canister.

Your system is putting a vacuum on the tank, which you don’t want. And when the car sits, tank fumes simply enter the intake manifold. Not only will it smell, but it may be hard starting the car.

JP2 is right. If you remove the carbon canister system, you may as well just vent the tank to atmosphere. If you don’t want to do that, you need to plumb in the canister somehow.

If you search October 2022, I redid my Charcoal System. I got rid of the Rochester valve, and used an electric valve instead. I still maintain the 1psi relief valve too. The Charcoal Canister fumes are only allowed out into both intake manifolds when the engine is running and during throttle intake.


Excellent info. I suspected it wasn’t as simple as pulling off the canister and plumbing into the manifold. I’ll check the October 22 article.

Title was Damn Rochester Valve.

Here is a photo of my final setup. Still seems to work great.

The big line that takes the fumes to the intake manifolds has a vacuum switch inline that you can’t see. It stays closed. A vacuum line to the top of throttle taps opens it. So fumes only are let out when I’m opening throttles while driving. I figured that’s a great time to release any fumes. Not during idle, and not when engine is off.
The electric valve I spliced into O2 sensor. So it allows the tank to vent whenever engine is running.

I did all of this because the new Rochester valve I installed a few years ago got stuck! My tank was not venting unknowingly to me, until I heard a loud ‘ping’ of metal, and heard the fuel pump straining. Luckily tank did not collapse and fuel pump is fine. I did not want to rely on a cheap Rochester valve after that.

And by the way, I tested venting to atmosphere by just leaving line from tank open in this area. The smell of gas fumes while driving and while sitting in garage is not worth it.


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This is an image of the canister and valves. The Rochester is partially hidden behind the hoses on the left , I am wondering what the two valves are on the right which seem to influence the vapours going into the canister from the tank.

That looks like a contraption only Jaguar could come up with. I’m going to have to have another go at mine for the third time. I’ve replaced the Rochester valve twice already, re-packed the canister with new charcoal and towards the end of last summer I go to gas up and whoosh, plus started to smell fumes again.
I just temporarily vented the cap until I can have another go at it in the spring.
You don’t know how close I am to tossing that whole setup over the hedge.

The complexity here are those two valves that i assume control when to release vapor from canister. If i recall, one is vacuum line controlled by intake manifold, and one is vacuum line controlled by throttle tap vacuum. I guess it distributes it better?

My system purges via throttle tap vacuum control only. I have had no issues with this.

And my electric valve replacing the Rochester valve, i am very pleased with it and the peace of mind.

Hello Greg, do you have any schematic drawing (diagram) for the set up you’re currently using.
I’m kind of interested.
It doesn’t have to be anything fancy but I would really like to put these issues to bed.

My photo is above.

No offence Greg i’m not sure i’m reading your photo correctly or seeing all the air piping and/or electrical details. If you have a hand sketch diagram, much appreciated! :+1:

Well I’m surprised this problem exists on the single tank XJS. It’s a very scary proposition having a quart container of raw fuel under the front fender overflowing and pouring raw fuel on the ground. Idk where the canister is on an S, but if it’s near any exhaust or ignition …well.
In the case of my s3 XJ6, i had return valves that would stick open, returning fuel to the wrong tank and when that tank was full, the pressure would force fuel through the vent system and fill the canister until fuel was pouring out. And like you say, it could be a quart or more of gas all over the pavement underneath the car. I’ll never forget the silver Craigslist xjc freshly restored, a few years ago that was advertised about two weeks before the owner reposted horror pics of the car with the rt front fender engulfed in flames, ended up burning the entire car. Wish I knew more about how to solve this problem. GM cars used practically the same vent canister and valves for decades and I don’t ever remember seeing problems with them.

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Greg, is the vacuum switch in the line not visible and existing vacuum switch?

I’ve included a copy and paste of your drawing, photo, and description of the photo, with my annotations. re my annotations correct?

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