Leaky AED - what do I need?

My AED has never totally worked right - it’s connected to a switch and when I turn it on to cold start it does give the motor a little more fuel and it starts for a moment but then the engine won’t run while it’s hissing. So it’s not super useful, which is OK. But now it’s started weeping / leaking around the base. The rest of the carbs are fine no leaks. Can anyone give me direction on what I need to order and what the process might be to fix? Do I need to rebuild the whole thing or just the seals around the big banjo bolt?

To my recollection, the junction at the base of the AED is a compression fitting I don’t remember a seal there. Have you tried tightening it? You might also check your float levels to be sure they are not too high. The richness of the AED is adjustable by the screw mechanism at the top which affects the needle location in it’s seat. Lower the needle to lean out. If you are blowing a lot of carbon on startup, you might try leaning the AED. My cars like the AED and I have to remember to switch it off.

Actually, I was wrong about that. There are seals and a banjo bolt so you should order those if tightening the bolt doesn’t help. Do you have a factory parts book? Very useful.

I have tried tightening it, no luck, so I will order some, it looks like red fiber washers.

The screw on the top is stuck… I have tried to adjust. And when the hisser starts it pulls the needle all the way down and it sticks fully open (likely why the engine conks out when the hisser comes on).

I guess I will take the whole thing apart and clean and try it again. Any other parts I should replace while I’m in there?

Burlen in UK have kits. Bought one for my XJ6. Paul.

yes, take it all apart

red fibre washers with non- hardening permatex seems to work, if you overtighten, it buggers the sealing surfaces, try stoning them off first

observe with magnification if the metal sealing ring and brass spring loaded valve make perfect contact, if the neck is carbonised or damaged they wont

The ASC work with incredible simplicity, it should give little trouble

I still dont like them, my manual chokes are a great improvement

Mine slowly didn’t work anymore.On disassembly the bracket’s orifices at the bottom were completely blocked with a watery mud. I took the AED off the carbs in situ(from underneath can be done) and had a lot of work to clean it out. ( Thank You ethanol?)


At the lower end of the solenoid you may find that the large banjo bolt is corroded into the AEC housing and the small banjo bolt is similarly corroded into the bottom of the float chamber.

If this is the case “hasten slowly”. In the former case the large banjo bolt will often shear off, in the latter case the thread into the float chamber is only about 6 mm deep.

In any event buy new banjo bolts, they are plated and that will help you maintain a tight thread clearance, if other parts are usable .Should these banjo bolts feel extra tight take the sensible approach and have a machinist machine out both banjo bolts. Hand him the new banjo bolts as a guide to the required cutting depths. The cost of machining will be far cheaper than the cost of parts if you have damage.

If you persist in trying to extract the banjo bolts you might be successful. On the other hand if the job goes wrong you will need a new float chamber, banjo bolts, bottom bracket, washer kit and a feed arm. I do hope you can strip everything cleanly but don’t try your luck too far as a couple of parts are sometimes hard to obtain. Effectively you will have stripped the unit by the time you have removed the banjo bolts as the main parts will have been separated.

If you want a 100% leak free AEC you can fit permanent fittings in place of the lower feed arm and banjo bolts and have a flexible hydraulic pipe connecting the fittings. This cuts out all the red fibre washers at the bottom end and ensures the assembly can be dismantled safely and cleanly. This arrangement allows a fitting to be bonded into the bottom of the float chamber where the thread is weak.

With some thought about the sequence, the carburettors are easy to remove, (replace the eight flange nuts with longer bronze nuts). With the carburettors removed it makes access to the small flexible rubber hoses that connect the AEC unit to the inlet manifold easy to replace. Owners often forget these hoses that are frequently leaking, but spend hours trying to set the AEC.

I presume from the image of your carburettors that they are on an Mk 2 or S type or are at least SU. AUD 154F /154R units.

Wow now you’ve got me worrying!

My carbs are HD8’s that were totally rebuilt, polished, etc. when I bought them about 3-4 years ago and have been in Southern California the whole time… so I assume / hope nothing is corroded and all should come apart as expected!

But I will certainly be careful.

Question for the group - are the fiber washers and other AED parts etc. the same on an HD6 and HD8? I was looking at XK’s and SNG for all the pieces but the parts drawings for a Mk2 are for HD6, my car has HD8s. I looked at the 420 and the MkX neither has a parts schematic for the ASC…

Hello Theo, you may be able to get definitive answers to your parts questions from the S.U. group of Burlen at The Worlds Sole Manufacturer of Genuine SU Parts - SU Carburetters since this is S.U. parts supply source and has online retail sales. In addition to very specific parts and rebuild kits they also have quite a bit of technical information online. If you exhaust their online technical library without finding your answers, they may be contacted directly.


You need an AUE 807 washer kit, large banjo bolt AUC2698. In addition you need the small banjo bolt, either AUC 1541 (most likely) or AUC4641 (alternative).

Yes the fibre washers should be the same, but you can check out my part numbers with your supplier. The numbers are all subject to change.

Two tips,

  1. As Roger McWilliams suggested deal directly with Burlen Systems now owners of S.U, and no other. No doubt you will get loads of suggestions….but think just where others are sourcing their parts……usual disclaimers.

2 You are dealing with an AEC (Auxiliary Enrichment Carburetter (Thermo), NOT an AED, which is a completely different animal. If you don’t use the correct terminology you are likely to get the wrong parts. It will also give you some indication of who might provide the right advice.

1 Like

Thanks. I did email Burlen, and they said the washer kit is the same for both carbs and gave me part # AUE 945…

I ordered all the parts from a US supplier based on the schematic for the Mk2 HD6 which looks just like mine. I guess I will see when they arrive!

If anyone is interested, I ordered a whole slew of little fiber washers and new banjo’s just in case, of course most of it was not needed. Loosened the big banjo bolt, popped out the two fiber washers, cleaned and dried everything, and refitted. First test drive and so far bone dry. Also freed up the adjustment for the hisser needle so will try to get that adjusted, but honestly don’t need it the car starts right up without it. Onto the next little task.

Hello Theo, recollecting you are in Southern California, here is a thought on use of starter carb for cold-engine enrichment. I’ve lived most of my life in SoCal and used to not bother with inoperative starting carbs since most days a car will start fine without and warm up quickly enough. The experience with that approach worked fine.

Maybe five years ago I got one of the Innovate air/fuel ratio diagnostic kits. Discovered on the car with AED not being used that I was running a little bit rich overall. Apparently my tuning to make sure cold start worked okay left it overall rich. Decided to tune to richness with warm engine and see how cold start was changed. Cold start got a bit more difficult to maintain and had some spitback/stumbling on acceleration when right after cold start. Activated AED with the new carb settings and overall felt improved. Now I use the AED every time, with an underdash cutoff switch and wired to have no hot lead in the carb area when switched off (Otter switch completely disengaged). Better running overall and reduced underbonnet fuel fire danger on the AED wiring.

Funny you mention. I have 02 sensors in both downpipes, and have my carbs adjusted for good mix when warm. They run quite a bit lean at first start up, so I hold the engine in a fast idle for a few minutes till it starts to warm up and normalize, and wait to drive it until it’s good and warm. But, now that it’s not leaking anymore, I might try to adjust it and get a little extra richness at first start!

Well, checked again today and now the same spot has fresh fuel on it… tried to tighten the banjo more and it won’t budge. Not sure if the gasket didn’t seat correctly? Or maybe the leak is actually somewhere else. Dried everything as well as I could and I guess will investigate more in a few days see if I can find the leak… UGH.

I purchased a used set of HD8s. I rebuilt the AED using brand new fiber washers and it leaked…out of desperation, I ended up reusing the original flat, very thin aluminum washers. no leaks. crossing fingers…Next time I will just buy the official AED rebuild kit.

Interesting. I ordered a bunch of different fiber and aluminum washers based on the different drawings of the carbs in different models. I used a fiber replacement as thats what came out of the old unit but maybe I will see if the aluminum one fits.

I am thinking I have seen aluminium ones as well

It is a good idea to examine the mating surfaces under the strongest light and magnification possible to inspect for burrs or marring,

carefully stone flat etc

I use an anti-seize on these threads