There have been 123 distributor retrofits to numerous older Jaguars, from 120 to recently XJ6 S3s

The original 123 distributor had 6-7 preprogramed curves to choose from.
The latest model is the + tune version where you input the Mechanical Advance curve and the Vacuum Advance curve (their terminology is MAP, Manifold Air Pressure)
All the Jaguar installations that I am aware of with fixed curve choices have been problematic, with product support lacking or confusing. See Mark 2 forum comment From a post on a Mark 2 on the forum.
Jaguar Mk2 1961
……” My distributor is marked „Jaguar XK 15-09-10“ (from 2010). Curve „0“ was set on the internal micro-switch. Contact with the manufacturer revealed none of the curves is optimal since they all start advancing the timing at a much higher rpm than the original mechanical distributor. They recommend using Curve ”0“ and set the timing at 8deg BTDC. I have done this but have the feeling that the engine is not running as well as it did with 5deg BTDC. I will try to optimize.
Hope this helps “

With the programable 123 distributor, the original curve data from Jaguar/Lucas distributor must be found, this can be difficult to find. If you are in the racing business you will appreciate the programable feature and would develop your own curves, not dependent on what Jaguar did with a manual or automatic transmission, US or UK octane ratings, compression ratios etc.
Just replacing a worn-out Lucas distributor with either 123 distributor, is not just plug and play.

If you are led to install a 123 distributor, I would only recommend the + tune model as you can eventually get to an acceptable solution.

For Jaguar owners needing to replace a worn-out distributor, with simplicity and a quality ignition system, I recommend the Pertronix D171618 and matching 45001 Flame-Thrower II 0.60 ohm ignition coil. This is plug and play, with the advance curves (conservatively) optimized for jaguar engine, modern compression ratios, and Octane ratings of available fuels. Use modern ignition wires and non-resistance spark plugs.
All of the Data is in the same format as original Lucas/Jaguar data. You just need to set static timing per Pertronix instructions. (Pertronix web-site recommends their distributors for carbureted jaguar engines only, but numerous installations by forum members confirm it will fire the EFI system from the negative terminal of the Ignition coil.) see attached distributor curves for Lucas vs, Pertronix.

XJ6 S3 I personally overhauled the Lucas 41912A distributor and upgraded the system, with the Pertronix 4 pin GM module (P/N D72000) in the Lucas Ignition amplifier. (This upgrade is approved in all 50 states). With the 45001 Flame-Thrower II 0.60 ohm ignition coil, I opened up the plug gap from .035 to .040" for a hotter spark.

Attached are curves for OEM Distributor installation and the optional curves for the fixed curve options from the 123 distributor. The 41912A Lucas distributor is for the XJ6 S3 EFI engine.

 

I installed a 123+ with Bluetooth and followed the programing instructions on the "Living With A Classic" YouTube channel done by Adam in Sweden and I've been very pleased. Car runs great. I have a 1972 XJ6.

Highly recommended!

Jeff H.

 

Jeff, Thank you for the link to an actual installation and math for the tune input on a Jaguar XJ6.
It cleared up the MAP math from "inches of mercury" to "kilopascal", then converted to "absolute kilopascal".
It also cleared up the initial timing on engine with only the centrifugal advance in the distributor, vs. "0" on crank with the total curve in the distributor.
Also noted both drivers were making changes after initial installation to improve low end, or high end performance based on their knowledge of how the car should preform.
Rgds
David

 

There were quite a number of changes through Series 3 production of the distributor advance curves, as well as different applications for different markets/ Emissions specifications. I have seen weights that range from 4 degrees advance to 17 degrees.

 

Quote:

Originally Posted by Jagboi64

There were quite a number of changes through Series 3 production of the distributor advance curves, as well as different applications for different markets/ Emissions specifications. I have seen weights that range from 4 degrees advance to 17 degrees.

The original ignition timing (dyno tested) as delivered, was based primarily on compression ratio, fuel Octane available, manual or automatic and pre, or post smog rules. If you are going to install a 123 + tune distributor, some research on original, or more desirable configurations (other counties) in the Lucas/Jaguar database is helpful. most everyone has had a reduction in fuel octane rating from date of manufacture, so initial timing and max mechanical can use some adjustment (2-3 degrees more advanced).
Example 1984 XJ6 S3 EFI (California car) octane recommended dropped to 87, at the same time a new vacuum unit was installed and initial timing and RPM increased 14* to 17* and idle at 700 RPM to 800 RPM.
This could have been done to tighten emissions up, or to improve drivability with the restrictive emissions requirements needed to allow sales in California. 1984 Jaguar still requires by-annual smog checks, so I keep my car totally legal.
My 1968 XKE was a California smog car when I acquired, after they dropped the by-annual testing, I took both the carburation and ignition back to 1967 UK specs, to regain lost performance (Also installed the original 9:1 pistons)
I made up a worksheet for my XJ6 and sent it off to 123 tech support to see if I am correctly interpreting their MAP requirements. They responded that I was interpreting the the math correctly. See attached.
If you are not in an emissions restricted state, then some research, will help you find the optimum timing configurations for input into the 123 system.
Note: If you have an early smog Jaguar with a "retard vacuum advance", you definitely need to move away from this, to an earlier, or later vacuum advance curve.
https://mgaguru.com/mgtech/ignition/...utor_specs.pdf

Rgds
David