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Eric Molenaar
New User
Username: aussiewraith78

Post Number: 22
Registered: 06-2021
Posted on Friday, 04 February, 2022 - 22:25:   Edit PostDelete PostView Post/Check IP

Hello all,
Just last week LRH32854 has not been coming down on engine idle from first start. I suspect choke related issue but the ambient temp here in Aus at the moment is average 27 degrees Celsius. She revs high and after a few mins i give the throttle a quick kick and that seems to make it worse.
So far i have sprayed all linkages with carb cleaner, removed anti run on and weakener solenoids, sprayed with penetrating oil bench tested with battery they click on and off put back on car. Took off auto choke solenoid checked wires a bit brittle but when bench test with battery had nothing happen. I think its supposed to energise and pickup your best sidchrome spanner.
However if i push the high idle cam anti clockwise with my finger the idle returns to normal but as soon as i hit the throttle the cam slips round clockwise and idles fast.
Do i need to reset the high idle cam as per section u in the manual or am i missing something.
As always thank you in advance.
Cheers Eric.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 749
Registered: 11-2017
Posted on Friday, 04 February, 2022 - 22:59:   Edit PostDelete PostView Post/Check IP

Workshop manual has a nice section for carb issues under Fuel and Carbs
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 2507
Registered: 09-2004
Posted on Saturday, 05 February, 2022 - 02:01:   Edit PostDelete PostView Post/Check IP

Eric It could be the stove pipe leaking or the set up of the bi metal spring, the spring could be broke.
just happens that mine is apart atm.



BTW it is not used running LPG for cold starting.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 750
Registered: 11-2017
Posted on Saturday, 05 February, 2022 - 03:29:   Edit PostDelete PostView Post/Check IP

The choke solenoid in the pic is extremely valuable and replacements do not exist. It gets magnetized by the choke on start relay. Having 2 black wires indicates it is not polarity sensitive, make sure you hear a click. If you find a used one that's cheap, grab it.There is also a gap adustment below it.
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Mark Aldridge
Frequent User
Username: mark_aldridge

Post Number: 771
Registered: 10-2008
Posted on Saturday, 05 February, 2022 - 21:55:   Edit PostDelete PostView Post/Check IP

Robert, I think there are solenoids on ebay which will fit . I bought one years ago as a spare, but have not tried to fit it. Basicly the same on my S1.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 751
Registered: 11-2017
Posted on Saturday, 05 February, 2022 - 22:42:   Edit PostDelete PostView Post/Check IP

As you may know, the stove pipes will corrode over time. Since they are covered one would not know, however they can easily be reproduced. Beware, the covering has asbestos.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 2514
Registered: 09-2004
Posted on Monday, 07 February, 2022 - 06:46:   Edit PostDelete PostView Post/Check IP

When I bought the car back in the early 80's soon after the failing of the choke due to incorrect operation, the stove pipes were tested by a firm shake of the corroded weak pipe breaking away.
Made up new ones from conifer.
No more probs to date and not needed running LPG.
The covering was replaced by non asbestos type.
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David Gore
Moderator
Username: david_gore

Post Number: 4064
Registered: 04-2003
Posted on Monday, 07 February, 2022 - 14:09:   Edit PostDelete PostView Post/Check IP

Cunifer is also known as 90/10 Copper Nickel alloy,

https://www.cunifer.com/

Highly recommended for automotive brake lines especially in countries where salt is used for de-icing roads in winter.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 2515
Registered: 09-2004
Posted on Monday, 07 February, 2022 - 20:31:   Edit PostDelete PostView Post/Check IP

Spot on David, the salt is a real problem with these cars in the UK.
Picture shows conifer pipe with cover slid back.

I spray copious amounts of old sump oil on the underside and behind the bumper over-riders etc.

Not allowed in the garage workshops and frowned when the mots are carried out.
Mine is not a garage queen how ever it still has its looks!
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 3264
Registered: 06-2009
Posted on Tuesday, 08 February, 2022 - 07:57:   Edit PostDelete PostView Post/Check IP

And a third, "Hear, hear!!," for cunifer.

All replacement brake lines I've ever made are cunifer. I'll never use mild steel for those again!

It's just so much easier to work with and its corrosion resistance is just icing on the cake.

Great for the other purposes mentioned such as the stove pipe, too (and I've remade these, as well).

Brian
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Eric Molenaar
New User
Username: aussiewraith78

Post Number: 23
Registered: 06-2021
Posted on Tuesday, 08 February, 2022 - 21:33:   Edit PostDelete PostView Post/Check IP

Update thus far.
Checked stove pipes by giving them a suck ( ive done some weird things but i didnt want to blow incase i hurt the engine) so i got to taste 50 year old Rolls Royce air,hopefully i will survive the night it was clear and no leaks detected.
I have taken my auto choke solenoid to a repair shop to see what they can do as it was not energised when connected to power and the wires were brittle and a few cuts in the insulation.
But reading on here on another threat i seen Patrick Lockyers great innovation of putting a spring on the choke butterfly to keep it from closing as that's what my problem seems to be when i use the throttle the cam slips back causing the choke to come on ( close butterfly) which increases idle and of course makes the mixture richer. Fingers crossed.
Thanks Eric.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 754
Registered: 11-2017
Posted on Wednesday, 09 February, 2022 - 04:46:   Edit PostDelete PostView Post/Check IP

The choke solenoid is magnetic. Test continuity. You will NOT hear a click when it is removed, only in situ. The choke on start relay should click to energize the choke solenoid on the air intake
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Eric Molenaar
New User
Username: aussiewraith78

Post Number: 26
Registered: 06-2021
Posted on Friday, 11 February, 2022 - 17:05:   Edit PostDelete PostView Post/Check IP

Good news gentlemen,
Firstly id like to thank everyone for their experienced comments. Unfortunately i am NOT a mechanic, rather tinker a bit and hope it works.
I can read and read and sometimes it makes no sense. This is my first car wit SU carbs and i think i am getting a grasp of it. The choke system i certainly am acquainted with now.
I cleaned and bench tested all weakener devices, removed debris from stove pipes with compressed air, the auto choke solenoid re soldered connections, removed choke housing cleaned bi metal spring and tested with hair dryer.
Put it all back together and is working correctly and no more high idle woes.
So tommorow will tackle the no.1 brake accumulater (replacing with disposable sphere and putting a kit through the accummulator valve assembly.
Thanks again and especially Ronnys garage for informative videos on you tube.
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Derek Atkinson
New User
Username: datkin21

Post Number: 6
Registered: 02-2015
Posted on Wednesday, 02 March, 2022 - 01:30:   Edit PostDelete PostView Post/Check IP

Hello everyone
After reading several posts on this forum and others, I’m looking to confirm my understanding of how the automatic choke mechanism works on my car DRH14432 (1973 Corniche). Since I purchased the car several years ago the choke has always taken a long time to completely deactivate, with the engine taking a long time to come off the fast idle, and I am now determined to resolve this.

Firstly, the choke stove pipes are in good working order and the tube in the exhaust is fine (also no soot on the choke thermocoil).

As I understand it, when the ignition is ‘on’ the choke solenoid will activate to hold the choke flap closed to prevent ‘fluttering’ during starting – I’ve confirmed mine is inoperative and have sourced a replacement – but my car has never had an issue with starting either.

Once running, the choke solenoid is deactivated and control of the choke flap positioning is taken up by the thermocoil, which is provided with hot air via the stove pipes. This in turn acts on the fast idle cam (mine is not sticking at all although I note there is some lateral movement along the shaft), thereby affecting the idle speed of the engine until fully warm, at which point idle speed is determined by the idle speed screw.

So far, so good I hope? Please correct me if I am mistaken.

Questions I have are as follows:

1. What is the purpose of the weakener ‘otter’ valve which sits behind the choke flap? Having disassembled mine it appears to be a thermoswitch which I assume measures ambient temperature given its location. It was also covered in oil, which I assume isn’t ideal for an electrical switch! Does this control the operation of the choke solenoid (i.e. deactivates it above certain temperature)? I thought the choke solenoid was controlled by a signal from the alternator to tell it the engine is now running.

2. What is the purpose of the scintilla switch (apparently located with other solenoids by the fan housing/voltage regulator)?

3. Fig K32 of the workshop manual which describes the ‘Fast Idle Mechanism’ includes a ‘vacuum retard tap’ which is completely absent from my car. Is this correct for a UK car?

4. The wiring in this part of the engine bay is starting to show it’s age and I’m not sure what should be connected to what. Can someone help me understand what should be connected to what so I can verify the integrity of the connections?

Further information, having inspected the position of the choke thermocoil it appears to have been adjusted to ‘lean’ versus the factory indicated V mark (itself right at the ‘leanest’ end of the dial).

The carburettors were rebuilt about 4 years ago by a specialist.

Any assistance would be gratefully received.

Many thanks
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David Gore
Moderator
Username: david_gore

Post Number: 4077
Registered: 04-2003
Posted on Wednesday, 02 March, 2022 - 09:50:   Edit PostDelete PostView Post/Check IP

Hi Derek,

Welcome to our forum and I note with interest your Corniche is a "sister" to DRH14434 which is no longer in my custodianship so I cannot provide any useful information in response to your questions using this vehicle as a guide.

One useful piece of information for you is you can significantly increase the engine performance using 95RON fuel by increasing the timing to 6deg BTDC [Before Top Dead Centre] and checking this increase does not result in "pinging" from whatever fuel you are using under hard acceleration. If pinging does occur, back off the timing 0.5degrees at a time until the pinging stops.

I used leaded fuel at the time so keep this in mind as unleaded fuel may produce different results and require a change in the settings I used.

For what it is worth, I could get rear wheel spin in all 3 gears with WOT [Wide Open Throttle] acceleration which "p*****d off" the "boy racers" at traffic lights. I did do a modification to the T400 GM auto transmission to stop the inbuilt clutch slip in 1st gear specified by RRMC for silky smooth starts at the expense of decreased service life of the 1st gear clutch pack in stop/start city traffic. This slip would become evident around the 95,000 mile mark for cars mainly driven in stop/start city driving and required replacement of the transmission 1st gear clutch pack. The transmission valve body modification to stop this inbuilt slip is detailed in the B&M T400 Transmission Kit Overhaul Manual below:

application/pdfAuto
B&M T400 Overhaul Instructions.pdf (13620.8 k)


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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 2306
Registered: 05-2012
Posted on Wednesday, 02 March, 2022 - 12:25:   Edit PostDelete PostView Post/Check IP

One of the problems with understanding the weakener and associated systems is they were being constantly updated to incorporate the move to greater emission control, so precise information for a specific model is hard to find. My car is a 74 Silver Shadow so may (or may not) be similar to your 73 Corniche. From what I have gleaned from various articles I will attempt to answer your questions and will hopefully be corrected by other owners if I am incorrect on any issues.

1) What is the purpose of the weakener ‘otter’ valve which sits behind the choke flap? - The weakener system makes the fuel mixture rich on cold starts or when the ambient temperature is below 57F. Above this temperature the weakener runs a lean mixture. As you mention, the thermoswitch detects the temperature and the fuel mixture is controlled by applying a small negative pressure inside the carburetor float chambers. This causes the fuel level in the carb jet to lower and lean the mixture slightly.

2. What is the purpose of the scintilla switch - The scintilla switch is a delay switch. When the ignition is turned on the choke solenoid is activated and earths through the scintilla switch. This switch has a small coil that heats a bi-metal strip. After a couple of minutes the scintilla breaks the earth connection and switches the choke solenoid off. The choke solenoid is a separate system to the weakener system. Some owners connect the choke solenoid through the starter relay so it switches off as soon as the engine starts.

Fig K32 of the workshop manual which describes the ‘Fast Idle Mechanism’ includes a ‘vacuum retard tap’ which is completely absent from my car. - the earlier cars did not have this - or a vacuum advance to the distributor.

The other thing to mention is the anti-dieseling solenoid. These cars are prone to dieseling after the ignition is switched off. This is where the engine carries on running, after a fashion due to the compression-ignition effects on a hot engine. It happened once on my car and it's horrible - sounded like the engine was being damaged as it spluttered, coughed and knocked as the cylinders fired at random. The anti-dieseling valve applies a large negative pressure to the float chamber to starve the engine of fuel and prevent dieseling.

This is all I can add at the moment. At some point I intend to spend some time and understand the various systems - maybe this summer.
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Derek Atkinson
New User
Username: datkin21

Post Number: 7
Registered: 02-2015
Posted on Wednesday, 02 March, 2022 - 23:17:   Edit PostDelete PostView Post/Check IP

Thank you David and Geoff for your help and prompt response.

David, I've seen you refer to DRH14434 in the other posts, and thanks for the tip about the timing. I tend to run Super Unleaded at around 98 RON as it has only 5% ethanol here in the UK. I'm lucky enough to have a Turbo R if I 'feel the need for speed' though.


Geoff, thank you for the explanations which now make a lot more sense! I'll check the functioning of the scintilla switch and ensure that it's linking through to the choke solenoid.

Presumably the 'otter' switch actions on a valve somewhere to direct a vacuum from the inlet manifold into the float chambers? There is a complex looking 'tree' with several vacuum pipes to and from it in the area behind the distributor. I've tested the switch itself by putting it in the fridge/freezer and it does seem to operate, although I can't test that it's calibrated to 57F.

I'm pretty sure there is no vacuum advance on the distributor (the car lives at my parents' place as I'm currently without storage space), so that would tie with the lack of a vacuum retard tap too.

Any idea where the anti-dieseling solenoid is located?

My car's symptoms are exactly the same as Eric describes in his initial post. My next task will be to follow the steps he has done and see if that cures the problem. I'll report back once that's done.

Many thanks for the help and advice, very much appreciated.

Derek
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 764
Registered: 11-2017
Posted on Thursday, 03 March, 2022 - 02:52:   Edit PostDelete PostView Post/Check IP

All your questions and an explanation of the "fuel tree" near the distributor are explained in the workshop manual. If you follow the hoses from the carb floats, they end up at the fuel column and then spill below the body.
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Derek Atkinson
New User
Username: datkin21

Post Number: 8
Registered: 02-2015
Posted on Wednesday, 09 March, 2022 - 02:40:   Edit PostDelete PostView Post/Check IP

Thanks Robert, I've had another read of the manual with my new found knowledge from the previous posts and can make a lot more sense of it now.

One further question, my 'otter' switch was covered in oil and I doubt making adequate contact. Assuming that was inoperative, it would make the car run richer, but would that then have the effect a causing the engine to run at a higher idle speed than it should until fully warm?

Thank you
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 2307
Registered: 05-2012
Posted on Wednesday, 09 March, 2022 - 07:24:   Edit PostDelete PostView Post/Check IP

Hi Derek

I personally don't think an inoperative otter switch would make the engine run at a higher idle speed - there must be another reason. The system is designed to run the richer mixture to promote easier starting. As the engine reaches normal temperature the mixture is leaned out slightly to give better fuel economy. So if the otter switch is inoperable the resultant rich mixture would be correct for starting and therefore would not cause the higher idle speed.
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Robert J. Sprauer
Frequent User
Username: wraithman

Post Number: 765
Registered: 11-2017
Posted on Wednesday, 09 March, 2022 - 08:20:   Edit PostDelete PostView Post/Check IP

Hi idle can also be contributed to a vacuum leak.There are many hoses and don't overlook the cruise control bellows. If in doubt you can plug the vac line to the bellows.

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