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MG TD TF 1500 - Spark Scatter on 2,3, and 4 - Advice needed Please

I have an unusual situation (unusual for me at least!) with a standard 1950 TD. The car is fitted with a positive ground pertronix unit and the car is positive ground.

Timing light displays a good steady spark on the number one cylinder, but 2,3,and 4 show varied degrees of scatter (or uneven spark).

The advance springs have a little weakness to them - but not much - overall condition of distributor is very good - tight bushings and the bowl is tight to the shaft. Plug wires are only two years old and are in good condition - they are the cloth braided/lacquer coated wires. I have a Lucas Sports Coil. Plugs are gapped at 30 thousandths (I understand that I can open them up a little with the Pertronix and the Sport coil).

I have read that solid core (stranded wire core) leads should not be used with Pertronix - is this correct?

Any thoughts on possible problem areas?

Thanks in advance

I had problems after fitting my Pertronix which (eventually) turned out to be the rotor. There seem to be lots of ideas about which rotors are good and which are dodgy, but maybe one of the experts here can advise you if you want to try a change.

For what it's worth, the photo shows the rotor which I used, on the right. I'm just waiting to be told I got it wrong......


David Provan

As I've been told, regardless of color, anything with a rivet puts too much spark too close to the inside of the cap and/or gives the spark a second jump-off point which doesn't sound good.


Knew it!

David Provan

It is certainly the case that solid core should not be used. Suppressor leads are the answer. If you access the BBS archives on this thread there is detailed advice from Bud Kreuger in response to issues I had with a pertronix unit posted in March

I'm assuming here that you are having trouble with the car not running properly due to the uneven spark

best wishes

G J Smith

Until last year's experiment with the LS (lobe sensing) version of Pertronix, I had run for about 14 years with hard copper ignition wires. Never a problem. However, I note from their spec sheets that Pertronix says that one should not be using hard wire cables, even with the original Igniters.
BTW, the LS version is outstanding. I've never before had such smooth acceleration right up to (and occasionally beyond) 5,000 rpm. It's been well worth the effort to create the set of suppressed cables. Bud
Bud Krueger

A good start to a cure, is to install one of these. PJ

Paul S Jennings

Hey Guys, thanks for the various comments.

I do have a good Schlemler red rotor - so I feel that component is OK.

I will make up a set of the suppressed wires as suggested.

Bud - what brand did you use and how did you attach the suppressed wire to the cap nuts - did you use the small disc and just bend the center core over the disc?

Bud - I don't see mention of an LS version of Pertronix on their website - I see Ignitor I and Ignitor II applications (are you talking about the Ignitor II)?

I created the set of cables by modifying the distributor end of a set of cable from NAPA. I used a cramping tool to connect the modified ends to the cables after slipping the nuts over the cable.

If you look closely on their website you'll spot some Igniters with the suffix LS. The one that fits our distributor is LU-146LS. If you insist on staying with positive ground you'll need to add the suffix P12, to be LU-146LS-P12.

Bud Krueger

If you have the earlier Pertronix (with the magnets you are OK}
If the lobe sensing one then Resistor spark plugs should achieve the same effect as suppressor wires and not have the hassle with the connectors.

I am using the early Pertronix with Bumblee wires and RN5C Champion plugs with resister (That's the R in the type) with great success on my positive ground TF.
Circuitwise the resistor in the plug should do the same thing as in the wire.
Don Harmer

This thread was discussed between 28/05/2015 and 29/05/2015

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.