Discussion
Anyone any idea where I can get an Automatic Enrichment Device (AED) for an XJ6 circa 1977 ?
The one on my car doesn't work correctly and the previous owner has already had it to bits.
Rather than buy a rebuild kit and then find out my own has been butchered (which is a possibility) I thought I'd get a used one and rebuild that as a straight swap.
Thanks
The one on my car doesn't work correctly and the previous owner has already had it to bits.
Rather than buy a rebuild kit and then find out my own has been butchered (which is a possibility) I thought I'd get a used one and rebuild that as a straight swap.
Thanks
I did think of a manual choke conversion but they appear to use the lower half of the AED anyway and I assume I'll still need an overhaul kit for the seals etc.
I'd prefer to keep the automatic function if possible although I appreciate that they never were the most reliable of things.
On the older units as fitted to Mk2 Jags etc. I seem to recall that it was a popular mod to fit a toggle switch on the dash so that the electric function of the unit could be over-ridden.
Would something similar be useful on the AED unit i.e. is it usually the electrical element that fails or is it the seals ?
To be honest I haven't really looked in detail at the unit yet and need to do some more homework
I believe mine looks something like this.
I'd prefer to keep the automatic function if possible although I appreciate that they never were the most reliable of things.
On the older units as fitted to Mk2 Jags etc. I seem to recall that it was a popular mod to fit a toggle switch on the dash so that the electric function of the unit could be over-ridden.
Would something similar be useful on the AED unit i.e. is it usually the electrical element that fails or is it the seals ?
To be honest I haven't really looked in detail at the unit yet and need to do some more homework
I believe mine looks something like this.
Don't take this as as the definative word as it's over 20 years since I worked on a carb fed XK engine but IIRC the earlier type auto enrichment devices (AED) on XK engines were solonoid activated, hence the bypassing switch.
Buried deep in the guts of the later design - S2/3 XJ? - is a bi metalic strip that's heated by exhaust gas and actuates a auxilary air bleed and fuel valves via adjustable cams. When cold, both valves are open and as the strip warms it gardually shuts them. In theory when both valves are open the AED supplys a richer mixture into the manifold suplimenting the air/fuel from the carburettors that gradualy leans out as the engine warms closing the valves and shuts off all together once up to temp with the carbs supplying all the mixture for normal running.
Th bi metalic strip gradually deteriorates and no longer completely shuts off the additional fuel/air mixture, meaning in normal temperature running the AED is still supplying a richer mixture than the engine ought to have. This is ruinious for fuel consumption causing lube oil contamination with fuel and eventually leads to bore wash and accelerated wear. Whilst all this is going on the engine is loving its rich luxury diet and will continue to cold start perfectly and run really well but it was not uncommon to find carbs that had been repeatedly adjusted by someone who found a over rich mixture caused by a failing AED and leaned the carbs out more and more to compensate rather than repairing the faulty unit that was the real issue.
My first XJ was a manual poverty spec S3 3.4 on carbs. Overhauling the AED and fitting a manual choke conversion to it together and with a few other modifications gave me a significant improvement in drivability and fuel consumption. On a run it'd nudge 25 MPG which was almost unheard of in Series XJ world.
If I ever had another Jag with a XK motor first thing I'd do is bin the auto part of the AED and fit a manual choke conversion.
Buried deep in the guts of the later design - S2/3 XJ? - is a bi metalic strip that's heated by exhaust gas and actuates a auxilary air bleed and fuel valves via adjustable cams. When cold, both valves are open and as the strip warms it gardually shuts them. In theory when both valves are open the AED supplys a richer mixture into the manifold suplimenting the air/fuel from the carburettors that gradualy leans out as the engine warms closing the valves and shuts off all together once up to temp with the carbs supplying all the mixture for normal running.
Th bi metalic strip gradually deteriorates and no longer completely shuts off the additional fuel/air mixture, meaning in normal temperature running the AED is still supplying a richer mixture than the engine ought to have. This is ruinious for fuel consumption causing lube oil contamination with fuel and eventually leads to bore wash and accelerated wear. Whilst all this is going on the engine is loving its rich luxury diet and will continue to cold start perfectly and run really well but it was not uncommon to find carbs that had been repeatedly adjusted by someone who found a over rich mixture caused by a failing AED and leaned the carbs out more and more to compensate rather than repairing the faulty unit that was the real issue.
My first XJ was a manual poverty spec S3 3.4 on carbs. Overhauling the AED and fitting a manual choke conversion to it together and with a few other modifications gave me a significant improvement in drivability and fuel consumption. On a run it'd nudge 25 MPG which was almost unheard of in Series XJ world.
If I ever had another Jag with a XK motor first thing I'd do is bin the auto part of the AED and fit a manual choke conversion.
Steve has got it right, but being a tad older, I'll stick in some more detail.
I replaced dozens, if not hundreds of these things under warranty. They were utterly appalling. You can rebuild and repair them all you like, but they will still bite you in the arse on a regular basis because the design is flawed.
It relies on hot air being convected all the way around the back of the engine from a small heat exchanger bolted to the inside of the rear exhaust manifold. This is done by way of a steel pipe coated with some heat insulating foam. The foam is of very poor quality and decays and falls off in an unacceptably short space of time. When it does the heat takes far too long to travel to the AED unit, especially in winter weather, and the engine runs very rich.
Inside the unit itself is a small diaphragm that controls the mixture valve, but it is exposed to the hot air from the heat exchanger and is quite simply not up to the job and perishes with the heat. When it does so you get full or partial enrichment.
Let me just make it clear how bad these things are. They were introduced in the late series 1 XJs and within months it was obvious this was a problem. The worst aspect is the effect of bore wash. This is when the engine is running so rich that the fuel washes the oil from the bores and you get premature bore wear to the point where the engine starts to consume huge amounts of oil. We had engines requiring a re-bore and new pistons at 8000 miles! Utterly scandalous design.
The only way to be sure with this is to bin it! The best conversion of all is to fit carbs with manual choke linkages and a cable. I used to use Rover 2000 TC carbs as they were also 2 inch and already had manual chokes fitted. It was a simple matter of fitting the cable to the dash and installing different needles to get the mixture right. After that you made considerable fuel economy improvements and the choke could be pushed in far earlier according to the weather. Most importantly, it didn't cost you an engine rebuild!
J
I replaced dozens, if not hundreds of these things under warranty. They were utterly appalling. You can rebuild and repair them all you like, but they will still bite you in the arse on a regular basis because the design is flawed.
It relies on hot air being convected all the way around the back of the engine from a small heat exchanger bolted to the inside of the rear exhaust manifold. This is done by way of a steel pipe coated with some heat insulating foam. The foam is of very poor quality and decays and falls off in an unacceptably short space of time. When it does the heat takes far too long to travel to the AED unit, especially in winter weather, and the engine runs very rich.
Inside the unit itself is a small diaphragm that controls the mixture valve, but it is exposed to the hot air from the heat exchanger and is quite simply not up to the job and perishes with the heat. When it does so you get full or partial enrichment.
Let me just make it clear how bad these things are. They were introduced in the late series 1 XJs and within months it was obvious this was a problem. The worst aspect is the effect of bore wash. This is when the engine is running so rich that the fuel washes the oil from the bores and you get premature bore wear to the point where the engine starts to consume huge amounts of oil. We had engines requiring a re-bore and new pistons at 8000 miles! Utterly scandalous design.
The only way to be sure with this is to bin it! The best conversion of all is to fit carbs with manual choke linkages and a cable. I used to use Rover 2000 TC carbs as they were also 2 inch and already had manual chokes fitted. It was a simple matter of fitting the cable to the dash and installing different needles to get the mixture right. After that you made considerable fuel economy improvements and the choke could be pushed in far earlier according to the weather. Most importantly, it didn't cost you an engine rebuild!
J
Intersting one this, I'll be keeping an eye on it.... my early S2 XJ6 4.2 manual still has its AED and seems to be workign fine, although having read the replies to the OP's question I'm now wondering if it's just masking some future problems big time. Should I bin it and fit a manual choke conversion or just leave it as it is...? It starts first time, every time with no hesitation... have I just got lucky...?
In Rover P5 circles it's very common to bin the factory fitted AED in favour of a manual choke, I still have the AED unit off my last P5B Coupe and it's a different shape and size altogether to the one fitted to the Jag. Are they just badly designed / ill thought out across all car marques...?
In Rover P5 circles it's very common to bin the factory fitted AED in favour of a manual choke, I still have the AED unit off my last P5B Coupe and it's a different shape and size altogether to the one fitted to the Jag. Are they just badly designed / ill thought out across all car marques...?
P5Nij said:
Intersting one this, I'll be keeping an eye on it.... my early S2 XJ6 4.2 manual still has its AED and seems to be workign fine, although having read the replies to the OP's question I'm now wondering if it's just masking some future problems big time. Should I bin it and fit a manual choke conversion or just leave it as it is...? It starts first time, every time with no hesitation... have I just got lucky...?
In Rover P5 circles it's very common to bin the factory fitted AED in favour of a manual choke, I still have the AED unit off my last P5B Coupe and it's a different shape and size altogether to the one fitted to the Jag. Are they just badly designed / ill thought out across all car marques...?
Pre fuel injection days it was the height of mechanical sophistication not to have a choke to nurse and carress on a cold morning as you splutterd down the road in a rich haze of petrol fumes - so AEDs or automatic chokes were quite the thing.In Rover P5 circles it's very common to bin the factory fitted AED in favour of a manual choke, I still have the AED unit off my last P5B Coupe and it's a different shape and size altogether to the one fitted to the Jag. Are they just badly designed / ill thought out across all car marques...?
I'd get rid - a manual conversion is much cheaper than a new engine and will pay for itself in saved fuel. I can't stand inefficient or crude engineering if it can be improved on, even it was the height of sophistication back in the day.
P5Nij said:
Intersting one this, I'll be keeping an eye on it.... my early S2 XJ6 4.2 manual still has its AED and seems to be workign fine, although having read the replies to the OP's question I'm now wondering if it's just masking some future problems big time. Should I bin it and fit a manual choke conversion or just leave it as it is...? It starts first time, every time with no hesitation... have I just got lucky...?
In Rover P5 circles it's very common to bin the factory fitted AED in favour of a manual choke, I still have the AED unit off my last P5B Coupe and it's a different shape and size altogether to the one fitted to the Jag. Are they just badly designed / ill thought out across all car marques...?
We have a P5B in at the moment for some repairs after some little scrotes vandalised it. It has been converted to a manual choke.In Rover P5 circles it's very common to bin the factory fitted AED in favour of a manual choke, I still have the AED unit off my last P5B Coupe and it's a different shape and size altogether to the one fitted to the Jag. Are they just badly designed / ill thought out across all car marques...?
The AED caused even more problems on the Rover V8 due to fuel contamination of the oil shutting down the hydraulic followers and causing premature camshaft wear. Rover only used them for around 2 years and then went back to manual chokes.
Although they are a different size the design and internals are identical to the Jaguar one, i.e utter crap!
J
Had a good chat with my local Jag man this morning and mentioned the AED, he suggested leaving it for now as it's not showing signs of trouble. The car is booked in for other work early next next month (new rad, hoses, electronic ignition and carb fettling) and he's going to have a look and clean the AED out just to be sure.
This is fascinating and explains why I got atrocious mpg (circa 8mpg) on my 1982 series 3 3.4. Sebring red no less.
Had to start the car with a small watering can of fuel tipped into the AED pipework.
I converted to manual choke, it became marginally easier to start but still rotten on fuel - I don't remember removing any part of the AED so perhaps that was where I went wrong.
Had to start the car with a small watering can of fuel tipped into the AED pipework.
I converted to manual choke, it became marginally easier to start but still rotten on fuel - I don't remember removing any part of the AED so perhaps that was where I went wrong.
For all who are interested, I am working on a manual choke conversion kit for all early Jags fitted with an AED unit.
It takes a bit of development because there are no less than 5 different SU carb variations across the range. But it will involve the total removal of the AED into the bin; the best place for it, and the fitment of a proper manual choke.
Watch this space.
J
It takes a bit of development because there are no less than 5 different SU carb variations across the range. But it will involve the total removal of the AED into the bin; the best place for it, and the fitment of a proper manual choke.
Watch this space.
J
jith said:
For all who are interested, I am working on a manual choke conversion kit for all early Jags fitted with an AED unit.
It takes a bit of development because there are no less than 5 different SU carb variations across the range. But it will involve the total removal of the AED into the bin; the best place for it, and the fitment of a proper manual choke.
Watch this space.
J
Any progress on this ?It takes a bit of development because there are no less than 5 different SU carb variations across the range. But it will involve the total removal of the AED into the bin; the best place for it, and the fitment of a proper manual choke.
Watch this space.
J
jith said:
It takes a bit of development because there are no less than 5 different SU carb variations across the range.
Is it just the different versions of the carbs you need to worry about?On the 3.4XK 150 there are 2 different versions of the inlet manifold connections from the starter carb to the main inlet manifold. I don't know about the rest of the range.
mph said:
Any progress on this ?
mph, Try this link.
http://www.solwayjaguar.co.uk/wp-content/uploads/2...
Its a common enough way of getting rid of the AED entirely, and the parts are available. The later HIF carbs as found on some S2 and S3's can be replaced with other units that have the manual choke linkages built in (so long as they are the correct size, and correct jets/needles fitted), or you can machine the originals to take the mechanism to move the jet from carbs as found on the Rover 3500.
Its one of the first things I've done on any XJ6 I've had as I hate doing 8mpg or having the carburettors spitback when it fails the other way. The cable operated 'over ride' you can buy for an AED works for a time, but only so long as the diapragms jith mentioned are intact. It only overcomes the hot air/bimetallic strip failure.
Probably the best thing for an AED is the distance test - in that you throw it as far away from the car as possible..
These look right to convert an AED car to a manual choke?
http://www.ebay.co.uk/itm/Rover-P6-2000-TC-CARBS-/...
http://www.ebay.co.uk/itm/Rover-P6-2000-TC-CARBS-/...
Huntsman said:
These look right to convert an AED car to a manual choke?
http://www.ebay.co.uk/itm/Rover-P6-2000-TC-CARBS-/...
Unlikely Rover/Triumph compatible variable jet carbs will even fit a XK manifold as IIRC the choke sizes and mounting stud pattern will be different, and even if they do actually bolt on they almost certainly won't be calibrated to accurately fuel a bigger capacity engine at part throttle nor will they be able to flow anywhere near sufficient air at wider openings. Different carburettors and engine vacuum conditions will also affect accurate vacuum ignition timing advance and retard.http://www.ebay.co.uk/itm/Rover-P6-2000-TC-CARBS-/...
If they are going dirt cheap it might be worth a punt just to see if it's possible to swap the manual choke components over - although I doubt it'll be possible - or make modifications to the original XK carburetors to get some form of manual operation working but you mess with air/fuel ratios and swapping or modifying carburetors at your peril and there's always the risk you'll end up running way too lean in certain conditions which eventually will kill your engine.
Without a proper rolling road set up and accurate exhaust gas analysis personally I'd not take the risk of running anything but the original carbs.
Edited by Jaguar steve on Monday 11th April 20:06
Jaguar steve said:
Huntsman said:
These look right to convert an AED car to a manual choke?
http://www.ebay.co.uk/itm/Rover-P6-2000-TC-CARBS-/...
Unlikely Rover/Triumph compatible variable jet carbs will even fit a XK manifold as IIRC the choke sizes and mounting stud pattern will be different, and even if they do actually bolt on they almost certainly won't be calibrated to accurately fuel a bigger capacity engine at part throttle nor will they be able to flow anywhere near sufficient air at wider openings. Different carburettors and engine vacuum conditions will also affect accurate vacuum ignition timing advance and retard.http://www.ebay.co.uk/itm/Rover-P6-2000-TC-CARBS-/...
If they are going dirt cheap it might be worth a punt just to see if it's possible to swap the manual choke components over - although I doubt it'll be possible - or make modifications to the original XK carburetors to get some form of manual operation working but you mess with air/fuel ratios and swapping or modifying carburetors at your peril and there's always the risk you'll end up running way too lean in certain conditions which eventually will kill your engine.
Without a proper rolling road set up and accurate exhaust gas analysis personally I'd not take the risk of running anything but the original carbs.
Edited by Jaguar steve on Monday 11th April 20:06
Ben, those carbs are identical to the one I converted last year and they are a steal at 50 quid. The only difference when these are fitted to a Rover is that the float chamber is on the same side of the carb body. This makes no difference whatever to the performance of the carbs.
The jets are identical to those in the Jaguar, but you have to use the needles from your old carbs to get the jetting correct. They are a straight fit onto the existing manifold and all you have to rig up is return springs and choke cables. There is a separate cable for each carb and they join together with a small junction box in the Rover. I usually contact Wadhams and buy a new Rover 2000 twin cable to make a job of it. Failing that you can use the twin cable setup on the S1 XJ12 if you can get your hands on one. Your original air cleaner also goes back on perfectly.
All you have to do after that is blank off the air intake on top of the manifold for the AED unit.
After you do this conversion and drive the car you wonder why the hell Jaguar bothered with the AED setup, believe me.
J
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