Electric fuel flow switch on AED

[stevewarbs]

When I got the car it was obvious that it was overfuelling and easily traced to the AED. A quick Google showed how problematic the AED can be so i disconnected it completely. Unfortunately though (as a newcomer to SU carbs) I didn't know that SU cabs don't have an accelerator pump and it is almost impossible to start the car without the AED.

I have been starting the car by manually pulling down the 2 jets in the engine bay whilst SWMBO starts the car. This is a problem when she isn't here.....

So, I have purchased a solenoid operated fuel switch and put it in the fuel feed to the AED and it works perfectly, car started first time and I then immediately switched off the fuel flow to the AED.

I already have the manual choke conversion fitted on the AED so the plan now is to lock the choke in the "on" position and then use a spring loaded switch to allow fuel to the AED to start the car and then release the switch to cut off the fuel supply, effectively an electric choke.

I will at some point overhaul the AED but this will remain a permanent solution for me. The overfuelling washes the oil off the bores and causes engine damage and the XJ uses enough fuel without chucking extra in

Total cost £13

[mike020150]

Ingenious! Mike.

[Tintin]

Very interesting.

How do you control the air flow into the carbs via the AED?

Robbie

[stevewarbs]

Very interesting.

How do you control the air flow into the carbs via the AED?

Robbie

As far as I can tell you don't. The AED just adds additional fuel downstream of the carbs.

Regards
Steve

[Tintin]

If your AED is the same as mine, there is an air pipe running from the back of the exhaust manifold, between the back of the engine and the bulkhead and into the AED between the carbs. The second plunger on the manual choke conversion regulates air in-flow by operation of the second cam. The fuel and air supplies to the AED are balanced/adjusted to provide the correct "mixture" for cold running. If the engine runs with the AED fuel supply cut off but the air inlet open, the effect will be much like a large induction leak and the mixture of the warm engine will be too weak. But yours may be different?

Robbie

[stevewarbs]

My understanding is that that is just to operate the bimetalic switch but on mine this has been removed and replaced with the manual choke conversions.

The idea is that as the exhaust warms up the air supplied to the AED progressively warms and operates the bimettalic switch which slowly shuts off the fuel from the AED. The effect is the same as on a manual choke where you gradually push the choke in slowly.

[Tintin]

All carburetted engines require additional fuel and additional air for cold running. As the engine temperature rises both the fuel and the air volumes are reduced by whatever gadget or system the manufacturer has deemed appropriate to fit. Re AED operation the XJ6 service manual says "On cranking the engine [from cold] air is drawn past the lightly spring loaded air valve (26) through the main valve seating (13) and into the inlet manifold". In the original AED there are two bi metallic strips - one for the air valve and one for the fuel needle. In the manual conversion there are two cams to replace the bi metal - one cam operates the fuel needle valve and the other operates the air valve.

To a certain extent the AED and carburettors are inter dependent - adjustment or modification of the former may affect the latter, hence the need for carburettor "tuning" after work on the AED.

Idle speed is another consideration. When I got my series 1, it was idling far too high giving an unpleasant jolt when engaging drive. The AED and carburettor adjustments were well out, but after a lot of research and re-adjustment the engine now idles correctly at about 700 rpm at all temperatures and both with/without the AED.


Robbie

[stevewarbs]

All carburetted engines require additional fuel and additional air for cold running. As the engine temperature rises both the fuel and the air volumes are reduced by whatever gadget or system the manufacturer has deemed appropriate to fit. Re AED operation the XJ6 service manual says "On cranking the engine [from cold] air is drawn past the lightly spring loaded air valve (26) through the main valve seating (13) and into the inlet manifold". In the original AED there are two bi metallic strips - one for the air valve and one for the fuel needle. In the manual conversion there are two cams to replace the bi metal - one cam operates the fuel needle valve and the other operates the air valve.

To a certain extent the AED and carburettors are inter dependent - adjustment or modification of the former may affect the latter, hence the need for carburettor "tuning" after work on the AED.

Idle speed is another consideration. When I got my series 1, it was idling far too high giving an unpleasant jolt when engaging drive. The AED and carburettor adjustments were well out, but after a lot of research and re-adjustment the engine now idles correctly at about 700 rpm at all temperatures and both with/without the AED.


Robbie

Hi Robbie

I'm not sure I agree with your first sentence. If you add air then you would have to add even more fuel as you would need extra fuel just to maintain the mixture and then even more to enrichen it. Also, Weber carburettors get a rich mixture by shutting off the airflow hence the term "Choke" and Twin Dellortos just need a coupe of prods on the accelerator and the extra fuel from the accelerator pump is enough to start the engine.

You might be right that air does go through the AED but that is probably just a vehicle to take the fuel.

Regards
Steve

[Tintin]

Hi Steve

If your modification does everything I think you are saying it does, I would be straight down to the patents office first thing Monday morning. And I'll pre-order mine now!!

Hope to see it in action at Gaydon soon.

All the best

Robbie

[jagmanuk]

Is your modification still working ok? Am I over simplifying, you just add an 'on or off' 12V solenoid in the fuel line to the AED which you switch off when the engine is at a suitable temperature?
Have you a part number and or supplier for a suitable solenoid?
Cheers Mike

[stevewarbs]

Hi Mike, it was working OK until the rear brake caliper seized....

It is just that simple I have the manual choke conversion so I have locked the choke on permanently, flick the switch to start and a few seconds later flick it back off again.

http://www.ebay.co.uk/itm/Petrol-diesel ... 25ddc4bde3

I also replaced all the fuel line with ethanol proof hose. There is a post on here, by Tintin I think.

Good Luck
Steve

[jagmanuk]

Hello Steve,

Thanks for your reply. I am going to try it on my S1 Daimler, which I think has suffered twice with failed AED's - both times a valve stem has snapped holing a piston.

Weirdly the link you show is the exact one I had found myself. I will get one when I can sort out my PayPal account which is somewhat screwed as I had to change my email address and when I try to login in it states there has been unauthorised usage.

The AED I have currently seems to be working relatively ok. The car starts straight away but it is difficult to tell if it shuts off or not. I have a pal who managed to purchase a new/refurbished AED from Burlen and had it fitted (total cost around £300) so the solenoid solution looks like a great idea.

As I understand it the AED has two valves controlled by the bimetallic strip, one for fuel and the other air, so stopping the flow of fuel would seem to do the trick. I am thinking it will be worth having the carbs tuned/set up once the car is warm to ensure things are ok and it is getting the correct fuel/air mixture.

Cheers Mike