Classic cars forum & vehicle restoration.
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TM8
Joined: 24 Feb 2013 Posts: 53 Location: Pretoria, South Africa
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Posted: Thu Sep 11, 2014 6:31 pm Post subject: Jaguar XK140 Carb Help |
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Hi,
Need some assistance I am trying to help a new owner of a Jaguar XK 140. The Car backfired and set alight after visiting the Carb Specialist need to say the wiring and paint work are now damaged.
I need help with the Wiring up of the Thermostatic switch as well as the thermo solenoid assembly. Some wires go to the coil which side positive and which negative.
We don't want to try the Carb specialist again after the disaster.
I am going to go through the two carbs and check they are done up correctly and check for blockages etc. First I will sort out the reason for the backfire. Any help on checking the setting of the Carbs?
How to check the Thermo side is working?
Maybe if some one has a photo to share of this area so I can follow through I think maybe the one Carb flooded and landed up igniting through the Distributor or coil not quite sure only assuming now.
Regards
Trevor |
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Old Wrench
Joined: 23 Dec 2013 Posts: 226 Location: Essex and France
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Posted: Fri Sep 12, 2014 9:49 pm Post subject: |
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The SU carburettors used on most Jags of this period used a separate starting carb or more correctly an auxilliary carburettor.
When cold the thermostatic (bi-Metal) switch enabled (powered up) the starting carb solenoid, lifted the piston, which simply allowed neat petrol into the inlet manifold.
The inlet manifold should have a drain pipe: these often blocked, meaning neat petrol being retained in the manifold. One cough and that could well be the reason for the fire. Backfires are normally caused by very weak mixture, faulty condenser, air leaks between carburettors and manifold and/or manifold and head; poor valve seats, and/or incorrect valve timing and distributor timing.
The timing chain on the Jaguar XK engine often wore, as did the Reynolds hydraulic chain tensioner. A nasty slapping noise at the front of the engine would be obvious.
These auxilliary starting carbs were notoriously unreliable!
Usual practice was to re-wire the solenoid to a dash switch, to allow manual choke on/choke off.
Setting up SU carbs is quite simple.
Firstly, disconnect the linkage between the carburettor butterflies (throttle).
With the engine warm, and air cleaner removed, gently lift the dashpot piston slightly; if the engine stalls or "hunts" enrichen the mixture by simply opening the jet carrier (by unscrewing the brass jet holder at the bottom). Mixture is correct when the engine revs increase slightly and then settle back down. Repeat for other carb/s.
Next, listen with a tube placed just into the intake orifice (the bit the air cleaner mates too). Balance the "hiss" to sound identical for both/all carburettors.
Open or close each carburettor's throttle screw to adjust vacuum depression (hiss).
You can use a a carb balancer for this: correctly called a depression meter.
e.g. http://www.scparts.co.uk/sc_en/synchrontester-22629.html
http://www.moss-europe.co.uk/Shop/ViewProducts.aspx?PlateIndexID=10783
Once the balance is correct, tighten the throttle linkage between the carbs.
This should assist you:
http://sucarb.co.uk/technical-chokes-thermos-auxiliary-enrichment |
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TM8
Joined: 24 Feb 2013 Posts: 53 Location: Pretoria, South Africa
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Posted: Sun Sep 14, 2014 7:47 am Post subject: Thanks |
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Thanks for the help.
Will check for blockages and read through the literature.
Regards |
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47Jag
Joined: 26 Jun 2008 Posts: 1480 Location: Bothwell, Scotland
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Posted: Sun Sep 14, 2014 10:19 am Post subject: |
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Trevor,
I'm guessing that the engine didn't have air filters/cleaner fitted. I don't think it would have caused a lot of damage if it had.
Art |
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peter scott
Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh
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Posted: Sun Sep 14, 2014 12:43 pm Post subject: |
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Hi Trevor,
This might help with setting up the starting carb.
http://www.nostalgiatech.co.uk/New%20page%2018.htm
The wiring is simple. The power from the ignition switch connects to one side of the solenoid (doesn't matter which side) and the other side connects to the thermal switch.
Peter _________________ http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon
Last edited by peter scott on Sat Apr 09, 2016 8:08 am; edited 1 time in total |
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Old Wrench
Joined: 23 Dec 2013 Posts: 226 Location: Essex and France
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Posted: Sun Sep 14, 2014 7:42 pm Post subject: |
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Lovely pictures on your site, Peter: and a lovely car, too.
My late father ran SS Jags through the late 30s and the war (would you believe with a gasbag on the roof!); and in the late 40s switched to a Mk V saloon. And thereafter to a succession of Mark VIIs and then a Mk. IX.
And thereafter, after a mini-flirtation with the then new Standard Vanguard, a MKII.
Which was probably where I gained my own love of Jags........
Nothing quite a dose of nostalgia to promote a big.S I G H.
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peter scott
Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh
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Posted: Sun Sep 14, 2014 8:44 pm Post subject: |
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Thanks OW. If you have any photos of your father's cars I would love to see them and I'm sure others woul welcome them too.
Peter _________________ http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon |
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Old Wrench
Joined: 23 Dec 2013 Posts: 226 Location: Essex and France
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Posted: Sun Sep 14, 2014 9:36 pm Post subject: |
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I do have a picture of Dad's wartime SS, Peter, replete with gasbag on the roof.
Trying to find the time to sort out zillions of of photos from my late mother in law and my mother who passed away only a few years ago......
I also have a picture of my wife's uncle's GN sports car, dating back to the late 1920s or early 1930s: quite a story with this one!
As always, it is time.
Has always amused me, BTW, how Bill Lyons changed the name from SS (Swallow Sideacar) to Jaguar, post WWI since the connotations of "SS" were probably not the best selling point thereafter!
Williams Lyons: one of my heroes; as was "The Jag" in Coventry. |
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