Manual choke for XJ6 Series 1

Having lived through the AED and its manual conversion I’ve moved to entirely manual with a small list of parts. The pictured jet pull system only works on one carb (HS8). I thought I would try this simple way and see if I need to work the fast idle as well. It works pretty well settling to a 500rpm idle quickly which builds as it warms up. Won’t be bothering with fast idle any time soon - would need somewhat more than I have here. Paul.

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The reason for the fast idle is to overcome cold engine drag, Paul - ensuring enough power, rpms, for the engine to idle. If it can’t idle - it won’t start…

Typically, as engine warms up, the idle will rise as cold drag is reduced. In colder weather, your arrangement might be insufficient as it only fattens the mixture, but low idle can be mitigated by increasing set idle - up to a point…

Nothing wrong with your experiment of course, but using only one carb leaves 3 cylinders running lean - and you may have some trouble driving off until the engine temp rises…

In this warm-up phase the lifted seat disturbs the carb’s programmed mixture control. The original AED was really an extra carb, providing both mixture fattening and enhanced idle - gradually disengaging with engine temp. Leaving the carbs adjusted to properly run a warm engine…

Another choke method use a combination of needle seat lifting and opening throttle butterflies…so…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Hi Frank, I will see how it goes. Sydney, as you will understand, does not have much of a winter. My cars usually get a bit of a warm up just moving them around to get them out! I have in mind a variation of the pictured that will lean on one idle arm - and through the throttle shaft - the second. So far so good after a few cold starts. Paul.

I’d be interested to know Paul, how your set up compares in operation with the AED manual conversion. I have been playing about with mine for several years and eventually reached the conclusion that the AED conversion (with some tuning and modification) was as good as it is likely to get…


Paul, I believe that this will work as long as you are careful on start up and driving off. Many years ago I bought the full kit for the HS8 manual choke that lowers the jets. Initially I only installed the arrangement on the aft carb. No fast idle fitted. It worked OK. Later I decided to fit the cross shaft to the fwd carb. Still I did not fit the fast idle stops. Works great for me, even though I have the carbs set very lean for economy. The fast idle levers are still sitting in the box unused.

As you know Frankie the manual conversion overrides the automatic management provided by the AED. The cable operated cams act through tappets the work air and fuel valving - a third carb as Frank says. This air and fuel is delivered into the top of the carbs beyond the butterflies by the split pipes.
My AED must have developed an internal failure as it was overfueling.
My crude system just uses the pull from the choke cable to lower one jet enriching the mixture for three cylinders. Other cars’ chokes do similarly but also provide a fast idle from the same choke cable. I don’t have this feature yet and won’t bother if I can avoid it! Paul.

Thanks John, that’s good to know. In desperation I could strip and refurbish my AED which had worked quite well for a few years. Will see how I go. Paul.

I do have the full setup and its very good,

however the idle situation can just be dealt with via the foot on the pedal

there are a few alternatives with the dual choke, including a twin cable, as used on the V12 (can still be ordered new), or fitting an arrangement such as that done by Ian (I think), another lister with his 3.4 conversion on the Saloons forum

It seems OK so far. The AED had to go, it was leaking fuel with the fuel valve fully shut off. Hard hot starting and unreliable. As you say Tony, a bit of right foot. Paul.

My experience is that fast idle is more important than mixture once the engine fires. As I expect you know, the AED fuel jet is adjustable. You can, with a bit of adjustment and modification (and a non-flooding AED), get full control via the conversion kit pull cable and cams. Mine gives about 1,500 rpm immediately after firing from stone cold on full choke (cable right out); within a couple of seconds pushing the knob in about 50% reduces rpm to between 500 and 1,000. There is plenty of power to accelerate away without waiting for warm up. Idle at hot in neutral is IRO 750.

I bought the parts to pull the HS8 jets down but never got round to fitting them - the AED modification was much easier.

See this…



great work! And judging from my 30+ years of experience with HS4 manual choke operation I’m convinced you’ll do just fine. Not raining into your parade, but our lister Keith Turner has basically re-created a full-choke mode for twin SU HS8 carbs, using just original SU parts from Burlen and operating on the jet seats of both carbs, IIRC. Very impressive work, neat and, again, no doubt, perfectly functional. For my skills it seemed a bit over-ambitious, so I stuck to the “easy route” my PO had walked before:

I do know that the SI enrichment device is different from SII AED, I’m not entirely clear about how … so take all I write with a grain of salt …For SII cars it seems though as if, despite the generally accepted shortcomings of the AED unit, the “full manual choke” has not become common. Most people make use of the aux carb as pre-installed, but replace the vulnerable hot-air-duct supplied and ageing bimetallic strip-operated “upper part” with the manual operation via wire and a dual-cam shaft operating an air and fuel valve.

These gadgets are by no means simple though. In fact I had a hard time with poor cold running properties over years until I went into the setup my PO had installed and found that he hadn’t got the cam lash right. For fuel it is 0.30 ins (0.76 mm). Correct installation makes a world of difference.

Good luck


75 XJ6L 4.2 auto (UK spec)

Yes, mine did this until recently - maybe I have a diaphragm problem? After watching fuel pour out in a service station forecourt and very hard starting I thought that I would try something simpler.

It was actually the first time I think that I have ever cancelled our journey and limped home - good lady wife and all. She has to understand - she had the car before we were married. Paul

The situation for S1 cars is similar - we abandon the upper auto parts for a manual override as you say - must be similar/same. Here is a picture of mine on the bench.

This is the younger of two that I have. The other thing that I have noticed is that the occasional “stumble” that I had at idle,k that I could never tune out, has now completely gone. I had set up the fuel with the 30 thou setting that you note by grinding the tappet. I think that I will strip both AEDs and make one out of two and store. For the moment I like the simplicity. As others have done I might develop a fast idle system as well. In Sydney it doesn’t take much to get them to start and run. I recall reading that the AED was designed to start a car at - 30 degs C and drive off in under a minute. A really cold morning here is 6 degs C! As Tony says a bit of right foot and I can drive away in a couple of minutes. Paul.

My recent purchase of a 1973 model xj6 was interesting when I looked under the bonnet and saw that ‘thing’ between the carbs. Had not come across anything like that except on my 1954 XK120 where there was this ‘choke’ and it was much smaller and supposedly gave a rich start mixture. Mine never worked. I’ m with the members on here and will probably lose that item when I get into starting the car and getting it running to see how good an engine I bought. The other item is the secondary throttle assembly. Can this be removed to eliminate the double butterfly stuff. I think it was mainly for pollution and not to enhance the performance of the engine. All advise greatly appreciated.

What carbs do you have, early S1 XJ6 had HD8 carbs, and a cylindrical ASC
(cannot easily be modded for manual choke)

later versions have HS8 carbs, with a rectangular AED. These can be modified several ways

I am not certain, but I remember the HD8’s and these look quite different, so probably HS, and the thing in the middle is rectangular. Can you tell me about the mods to make the choke manual? thanks. ron

One way is per my picture above. The gold part is an aftermarket adaptor that operates the calving inside the AED manually, rather than using heat signals coming via the pipe connected to the rear exhaust manifold. It’s the body of the AED - below the gold part - that is playing up on my unit at present. Paul.

they will be HS8s then, (you can observe a lever that allows the jet to be lowered from the lower outside)

method 1)

  • buy a kit that allows manual adjustment of the rectangular AED…as mentioned by Paul, Google for kit price

  • do what Paul has done now, and manually choke one carb

  • do what others on here have done, and fab up extra parts to make it work on both carbs

  • the ultimate is to have complete control over jet height and idle speed on all carbs.
    The complete kit is NLA, but most parts can still be purchased from Burlen SU

Certain other vehicles such as Volvo had HS6 manual choke carbs…its is possible to rob some of the NLA parts off them, and use Burlen and generic items to make the complete system for HS8

I have a triple HS8 setup made this way, yet to be fitted

It seems that the Brits have a penchant for making things more complicated than need be, and it is if they have some German blood in their veins. It is a delight to see some of this stuff, and if it actually keeps working, all the better. But we know how that works out in the long run…I think surgery is in order.

I have a notepad data file with a lot of Burlen part numbers and links to do this conversion.

If you want I can PM it to you

(there is link to a pdf that says security risk, but it checked out ok)

I could post the info here too if others want