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Hi all. I am running a 1976 Daimler 4.2 coupe with twin SU 8 carbs and a newly fitted auto enrichment device.

The car was still suffering from flooding, at the time, I also had an exhaust manifold leak so I took the car to my local mechanic, who promptly diagnosed the exhaust leak to be the cause of the AED problem (not enough hot gas telling it the engine was up to temp)

I have since had the car back and it has ran fine for a couple outings around 75 mile in total.

So, on a run through town yesterday, it started to give the same symptoms again ie tickover dying off, needing to slip in to neutral and rev up, lots of blue smoke etc I managed to limp home and lifted the bonnet , and manually kept the revs up while I had a look and listen.
There was nothing obvious to see but I could make out a noise I can only describe as a small electric motor running flat out... There was too much overall engine noise to pinpoint the source ..
So anyone got any ideas or theories? After the new year break I'll contact the garage again but thought I would post this in the meantime. I'm also thinking of fitting a manual choke kit, does this make the AED redundant ?
Thanks in anticipation
Steve Ross.

Hello Steve,

I'm not familiar with the AED but the exhaust blow surely would not stop the manifold heating up?
My S.U. manual just says that the hot air pipe from the rear manifold needs to be sound (airtight) at the manifold and AED connection and the lagging should be intact.

However, there is also the possibility that a carburettor is flooding and the AED is not the cause.
Remove the dashpots and switch on the ignition, (disconnect the coil if it is going to be on for some time) and see what fuel level you have at the jets, it is normally about an 1\8" below the top. If there is a problem you may see petrol overflowing into the carburettor choke?

Alec

Re the sound of an electric motor, the noise is probably from the battery fan. Although the fan should only run when under bonnet temperatures are high, the bimetal switches are crude devices. They can be opened and altered by bending which may involve lots of trial and error to get it to work at an appropriate temperature. Alternatively, if it offends the ear unplug the wires attached to the front of the battery box! Mike.

I'm also thinking of fitting a manual choke kit, does this make the AED redundant ?Steve Ross.

It depends on exactly which kit you fit, but the one I got needed the bottom half of the AED (the metal part, not the bakelite ones.) The lower diaphragm is retained.
Picture here:

I never got it to work very satisfactorily and, if I could have replaced the bits of broken bakelite, would have been much happier to have kept the AED. However, setting one up correctly is fiddly and time consuming.

Which sort of carbs do you have ? (SU 8 isn't quite definitive) The HIF7s don't have provision for a manual choke, but some of the earlier ones (HS and HD) do and fitting a cable to this might be an alternative?

Please be careful messing about with bimetal switches.

Mike states that the bimetal switches are crude devices but this comment is far from the truth. The bimetals found in such switches are precision calibrated prime movers carefully designed and manufactured in order to switch off at a preset temperature and to reset at another preset temperature. Furthermore, the switches are designed with a snap action operation to give instantaneous opening and closing of the electrical contacts.

If you start messing about with the bimetal then you are asking for trouble. First, you will probably alter the break temperature to a figure different to the initial setting. Second, you will almost certainly alter the re-make temperature to a point that would make the switch cycle either too quickly or too slowly. Perhaps worst of all though is that you will probably cause the switch to lose its snap action, resulting in a slow break and remake of the contacts leading to contact overheating, burning out and eventual failure of the device and possibly causing a fire into the bargain.

Don't be fooled by the apparent simplicity of the devices, they are thoughtfully designed and engineered to perform their intended function. They are still the most positive and cost effective means of switching high current whilst protecting sensitive circuits from overheating. Just about every motor used in every car, vacuum cleaner, oven etc. will be protected by a bimetal device.

I will guarantee one thing when it comes to a bimetal switch - if you mess around with it then you have just ensured that it needs replacement. Would you risk your car for it?

Yours

A Bimetal Bore

Hi all and many thanks for your replies.
So far I have discovered the following, but not yet resoved the problem.

Under the bonnet yesterday, I discovered the following.
The hot air pipeline from the exhaust manifold to the A.E.D was totally unlagged ( now re lagged )
The source of the Motor noise was infact ... The short section of rubber hose connecting the hot air pipe to the A.E.D had slipped off the tail from the A.E.D and was just butted to it ( slack jubillee clip ) and the suction was making the motor sounding noise and pulling in cold air. After refixing the hose I thought I had solved the problem, but the simptoms again surfaced after a short run.
So another hour or so looking and tweeking led me to the inline fuel filter just befor the Carbs, it was very very dirty, I had a spare handy and replaced it , I opened up the old one and dear me it was horrid !

So I now believe I simple have a pair of shi77y carbs, I am ordering a gasket set and will be stripping and cleaning in a couple of weeks time, I will keep you posted on the next outcome
More or less convinced it's not an A.E.D problem now though.
Cheers Steve..