Automatic choke problem

[Sam01]

Hi, I have a problem with the starting carburettor on my 1968 3.4 S-Type, in the last few days it seems to not be working (no clicking) when I use the on/off switch under the dash. So far I have tried the following.
1. Taken the solenoid off and connected it the +/- terminals on the battery and it operates.
1. Replaced the solenoid back and reconnected the green wire to it and then run a spare wire to earth from the other terminal and it operates, but it is on all the time regardless off the on/off switch.
So hope someone could point me in the right direction to get to the bottom of this.
Many thanks

[cass3958]

Sam could be a couple of things which depend on the wiring system you have used to the extra switch.
To explain the normal wiring system for the choke you have a live wire going to one side of the solenoid which is operated by the ignition switch. The second wire is an earth that goes through the Otter switch. The Otter switch is a Bi Metal switch that sits on the top of the inlet manifold just behind the thermostat housing and has three small bolts holding it down and a single wire connector on the top. The Otter switch works on heat so when cold it is creating an earth and the solenoid works but when it gets hot, as the engine heats up, it breaks the circuit and the solenoid stops working switching the choke off.
The Otter switch has always been the main problem with the automatic enrichment device (AED/Choke) as this can fail either way leaving the AED permanently on or permanently off.
Now depending on how your system is wired up it could be the Otter switch has failed. (£40 for a new one from SNG Barrett with the gasket. https://www.sngbarratt.com/uk/#!/Englis ... 75336a44f2 )
I am assuming that the way your new switch is wired is that the power from the ignition goes to your new switch then on to the solenoid and the earth from solenoid goes to the Otter switch which has failed. I am only guessing this because when you put a fresh earth from the solenoid to ground it works but for some reason does not turn off with your new switch.
My only concern is that you say that even with this new earth connected it does not matter if your new switch is on or off it still operates the solenoid. If this is the case you will have to trace the wiring back from the solenoid to the switch and the switch to the live source to see where the problem is. It could be the new switch has also failed. These checks can be done with a continuity tester.
The joy of the S Types wiring system is that it comes from the 1960s and does not have electronic circuitry bits attached that make it impossible to trace a fault other than by replacing items.
Hope this helps but if not please come back and update us and perhaps we can sort it out eventually.

[Sam01]

Many thanks for your reply, the on/off switch has been fitted before the car came to me some 20 years or so, it has always worked till now. From the two terminals I have a green wire one side (power I think) and I think a black wire the other side, I have not traced where that goes as yet, maybe goes to the on/off switch, yet to trace.
I have a otter switch in place but there is no wire attached and never has if my memory serves me well, I was now thinking to disconnect the black wire and run a new wire from this terminal to the otter switch as normal, this may bypass the switch, at least I will find out if the otter switch works.

[cass3958]

Sam, If your Otter switch was disconnected then there is a possibility that it was not working which is why they put the bypass switch in.
Things to check.
1. Power is going to the new switch. If you find out which wire is live you could then follow this back to the fuse box. Should be easy to follow just by pulling gently on the wire and seeing which wire on the fuse holders behind the dash moves.
2. Power is crossing the switch when turned on. if not disconnect the wires from the switch and jump the wires.
3. Power is reaching the AED solenoid.
4. That the AED Solenoid has a good earth.

Once you know that power is going to the AED and the solenoid jumps with a good earth then connect the Otter switch to the solenoid earth when the engine is stone cold and see if this earths the AED and the solenoid still jumps. If it does you will then have to start the engine and get it hot and see if the Otter switch breaks the circuit and switches the AED off.

On my system I have a switch on the dash which I turn on to allow power to go to the AED and I can turn the AED off via this switch as soon as I start to drive. But if I leave the switch on by mistake, the Otter switch disconnects the circuit when the car gets hot and turns the AED off. This way I have no AED choke unless I switch on the dash switch but it does switch off automatically. I find in the Summer I do not need the choke to start the car so this system works fine for me.

[Glyn Ruck]

We cover standard wiring here if it helps:

http://www.jagstyperegister.com/forum_n ... 5185#p5185

[John Quilter]

I have a somewhat different solution than cass3958. I have an additional wire from the Otter switch to a toggle switch under the dash with a warning light. As intended the Otter switch works on cold start up but can be over ridden if it shuts the choke off prematurely causing the car to stall at intersections before fully warmed up. This permits me to turn the choke on momentarily as needed. Sometimes under high engine vacuum situations it is necessary to "blip" the throttle slightly to get the solenoid kick on.

John F. Quilter
Eugene, Oregon USA

[cass3958]

Yes the other option John. Your way you can use the choke at any time where as I cannot when the engine is hot and the Otter switch is off. Either method works I suppose it depends on the ambient air Temp where you live. Although we moan about British weather our Temperatures only vary from Minus 6 possibly once a year to plus 25 centigrade ( 21 to 77 Fahrenheit) so once our engines are warm there is no longer a need for the choke.

[Glyn Ruck]

Many permutations can work.

I find that many people don't set up the needle in the AED for their particular ambient conditions & then complain that the device does not work to their satisfaction.

Being analogue it's never going to match the perfect enrichment of EFI but it can be optimised to minimise engine stumble.

[johngosnell]

I was reluctant to change this post but what I would like to know when modifying from the automatic carb enrichment to the electrical switch override what is normally removed to allow the switch system to manually operate the choke. As Mine was already changed when I bought the car and you all know my medical situation I have never been able to investigate.
And if I ever decided to go back to the auto system what would be needed. info just for interest ( bored winter cold day!! )


Regards John

1B1257BW

[cass3958]

John you just have to look at the simple electrics that make the AED work. Power from the ignition to the AED solenoid with an earth created by the Otter switch and we have not really done a lot to alter this.

All we have done to make it manual override is to put a switch in my case between the live ignition and the AED so I can control the power. John on the other hand has fitted a switch on the earth side removing the Otter switch so he can control the earth by turning his switch on or off.

The main difference between the two systems is that if I forget to turn the power off my Otter switch kicks in when the engine heats up and switches the AED off for me. I cannot turn the AED on once my engine is hot.(As long as my Otter switch is functioning correctly) I did this so once the engine is running I can turn off the AED early.
In Johns system if he forgets to turn his switch off then his AED will remain on all the time and the engine runs rich. John can turn the AED on at anytime even when the engine is hot.