www.jec.org.uk

Hi all, has anyone done a conversion on their 4.2 ?
any comments / feedback
Thanks
Steve Ross

Hi Steve,

We use the 123 distributor system from SNG Barratts. Its great!
I have read a few bad reports on these -not working well etc. We have fitted 20 + systems, and if you set them up right - we have great results. Set the distributor on number 3 setting and time the car up properly - and it will start the car easier, you get a better advance curve, and smoother running!
I have had one unit fail, which SNG replaced under warranty no quibbles

Hope this helps?

Keith

I have the constant energy 45DM6 dizzy with an AB14 amplifier on both the XJ6 S1 and on my Challenger. Works perfectly and keeps the system somewhat original

Hello all,

looking at Baratt's description of the 123, I note in their blurb that they say that just replacing the points with an electronic module in the standard distributor does not compensate for wear. Now this is contrary to what is widely touted as being a good reason to fit such a device. It is something I've always suspected but that's the first time I've seen it in print.

Alec

Many years ago I fitted a Lucas electronic ignition conversion kit to my Series III. Was much better than most of the cheap ones at the time, with a replacement rotor arm carrying a metal shield with six segments cut out. The shield ran in the gap of a Hall-effect sensor, so it replaced the points completely. A fancy amplifier box completed the wiring. It ran without problem for about 10 years, by which time the car was dissolving into oxide

Having Googled a few kits just now, many seem to use the original points cam with some sort of magnetic sensor. IMHO that's not going to be as accurate as having a separate timing ring like the Lucas kit had. Lumenition have what looks a similar type, and like the Lucas one the gubbins fit within the distributor. It's somewhat cheaper than Barratt's 123, but as they point out, theirs replaces the timing weights - though I think that still leaves the vacuum advance, which always struck me as the most Heath-Robinson part of the mechanical ignition systems.

Hello Paul,

I think the vacuum advance is often misunderstood, but it is an ingenious device, (I note that the 123 has one according to the blurb but obviously different to the original set up).
To explain further, cars with vacuum advance have their carburation set up weaker in the cruise range than would be normal. This weak mixture requires more advance for smooth running, and as the vacuum is relatively high at cruise this is used, via the diaphragm in the unit to adavance the ignition. Simple and effective and helps with the fuel economy.
Although all Lucas vacuum modules look the same they are not and there are three figures stamped on them, start vacuum, max vacuum and advance degrees at full vacuum and are selectd by dyno testing to match a particular engine (As are the distributors, e.g., you can't just swop any 25D6 for any other, all distributors are matched to an engine.)

Alec

...
you can't just swop any 25D6 for any other, all distributors are matched to an engine.)
...

I think I'm clarifying your remark if I say that distributors are matched to an engine design/operating environment (e.g. XK 4.2 in fuel-injected car), not to an individual engine. It should be possible to swap distributors between similar car engines, but you need to start checking numbers if it's between different versions of the same engine or different uses, such as fuel-injected vs. carburettors.

My apologies if you are saying that distributors are tuned to an individual car.

Hello Paul,

you are right, I didn't make myself clear, it is not individual engines but individual models. Even then some manufacturers fit different specification distributors as time goes and minor modifications are made to the engine. E.g. Mk 2 2.4 and the later Mk 240 I would expect to have different distributors (Although I haven't checked) as the carburation and cylinder head was altered.

Alec