Startup is ok. Problems occure when the cold start carb disengage and until it is reaching 70degr C. If I shortcut the coldstart thermostat, it helps but this is not correct thing to do. Any members who has a solution for me?

 

You can purchase a new Otter switch with electronic modern innards that's supposed to work better.

OR

Just by-pass the Otter switch all together and wire a simple toggle switch underneath the dash somewhere.

 

I have exactly the same problem. The thermal switch opens before the engine is warm enough to run without the choke, but mainly in cold weather.
I set up a 3 way switch and an indicator light showing when the choke solenoid is energized. The switch positions are Automatic, OFF, and ON.
I cold start with the switch in Automatic and see how the engine runs as I drive off. If it tends to stall, I switch to ON until the engine temperature rises to about 65F and then go back to automatic. Having the light is a good reminder to manage the choke switch correctly.
I think there is significant variability in the need for choke depending on the ambient temperature and it is un-realistic to expect a single point switch to work appropriately under all conditions.
I would think a better automatic system would be based on both engine and air inlet temperature.

 

If I understand your question, the cold start carb works correctly, but after it disengages, the engine runs poorly until it gets to 70 deg C ?

The cold start carb should turn off at approx 35 deg C, if yours is doing that then it sounds like the mixture is too lean, by shorting the otter switch you are getting extra fuel so this helps obviously, but would not be the solution.

Check the mixture settings, also what does the engine run like under load after it has warmed up fully ?

 

Like many others, I have fitted an on/off switch on the dash to help with Jaguar's "Automatic Enrichment Device".

I like your idea of a 3 position switch with warning light.
Any chance of you sharing your wiring diagram with us?
Thanks!

 

As Red Triangle asked here are a couple of pictures describing the choke wiring I made up.

This was part of a complete rewire with a new harness that featured other changes like multiple fuses, alternator, hazard warning etc.

 

Thanks a lot, this is exactly how it works. I shall try to check the ignition before I move on to carbs. have a nice day.

 

Assuming your ignition is perfectly timed and in good shape, I do not see what you can reasonably do the carb's. After all the only adjustments available are to set the idling speed and mixture when the engine is up to temperature.
I suppose you could have wrong needles installed or else a worn jets but if the car runs fine when warm then this seems unlikely.

 

Actually on further thought, perhaps the Automatic Enrichment Device could benefit from tweaking.
I got the best result by carefully following the procedure in the SU Workshop Manual. A copy is attached.
This procedure is more explicit than written in the Mk2 shop manual.

Good luck

 

This was my point, if the problem is when the AUX carb turns off, either the AUX carb is turning off too early i.e <35 deg C and the Otter switch is defective, or the car is running lean, adjusting the AUX carb will only effect what happens while it is on, not when it is off.

In order to know what advice to give we need to know how the car runs when it is up to temperature, Jagmk21964 states that it runs better if he shorts the Otter switch, that again indicates either that the AUX carb is switching off too early or the carb/s are lean, he also says that it affects running up to 70 deg C , I find it odd that the engine has to get up to 70 deg before it runs Ok, and would personally suspect that it is under powered too even at temp.

 

Very neat set-up. Thanks for that.

 

The original set up stinks, the repro otter switch stinks.
The whole set up, really never worked.
My 3.4 runs perfect.
Put a switch under the dash which I posted the entire set up about a year ago.
My car starts like its fuel injected, you can time the choke with the switch by the gage and cut it out whenever you like.
New plugs, check your timing and away you go.
Astons at the time got smart and had a switch on the dash!
Of course if the solenoid switch is working and set up correctly

 

Yeah, I agree with you, it's actually a pretty **** poor design.
Even by-passing the Otter switch, if it's parked outside in the fall, lets say, and it gets colder then normal that night, it probably won't start.

You then have to adjust the actual needle valve in the system so that it gets more fuel to run when it gets colder.

On my car the air cleaner duct is in the way, you can get at the needle valve, but not easily.
A typical poor British design.

 

Yes, perhaps, by today's standards, & cars which now have the benefit of electronic sensors and IC chips etc.

I can handle faults in 50 year old designs. What I can't handle is moderns which need new brake disks after 50,000 kilometers and plastic parts in automatic transmissions which fail & render the car uneconomic to fix. Also general faults dealers won't/can't fix & manufacturers wash their hands of.
(Spleen satisfactorily vented!)