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MG MGA - Timing Light and Pertronix

I am having trouble getting my timing light(s) to operate with my system. I bought a new timing light and that doesn't work well either. It's intermittent and even straight off the coil it stops working at higher revs. However, I have had a very useful conversation with Paul at Aldon Automotive.
This is a common problem if you use copper leads and the old resistive caps with a pertronix. The ignition works ok but you can't trigger the timing light!

Paul recommended changing to silicone leads a non resistive cap and resistive plug. This is purely to get the timing light to work. After setting it up it could be reversed back to copper leads and restive caps. I seem to learning a lot at the moment but what a faff! Any one else had a similar experience?




John Francis

You will probably now get all the comments that silicon / carbon leads don't or cannot work with side entry caps - in spite of my experience that it works really well (confirmed by Kelvin too). Just install the silicon/ carbon leads and forget that they are there - you will (hopefully) still be driving on them 20 years from now!

Dominic Clancy

The commonly used term of silicone leads is a bit misleading
The silicone is the outside insulator, your copper leads have probably got silicone outers
'Paul' should have used the term-silicone/carbon as
Dominic has-
there are other silicone leads like wire wound silicone leads etc so a more acurate description other than just simply silicone leads would/should have been from someone like Aldon

If you fit carbon leads into a side entry cap, it's a good idea to insert a pin into the centre of the end of the lead for the screw to screw up against and then you get the full length of the pin contacting the carbon string instead of just the end of the screw--which 'can' cause the string to burn away at that point and loose contact

willy
William Revit

Willy. Just got my leads delivered. I like the idea of the pins in the distributor cap. Do you have a suggestion for dealing with the end that goes into the coil? I am using an original screw-in cap arrangement which has a brass washer on the end of the copper strands. Perhaps another pin but bent on the end and using the old brass washer under the bend in the pin.
John Francis

Hi John
First off, using resistor leads 'and' resistor plugs together is putting a bit more load on the poor old coil, although having said that, with the petronix i guess that cancels it out a bit, but if you find you have a new misfire right up in the rev range, it'll probably be the double resistor setup doing it unless your coil is some high output machine and can cope---maybe drop the plug gaps back to 25 ish would help balance it out
As far as the coil lead goes, you could retain your wire lead, or find a tiny little screw about 3/4" long and screw it through the washer up into the core of the lead-It has to be skinny though otherwise it will expand the end of the lead and the acorn nut won't turn properly on the lead
If you have a look up in the end of one of your old resistor caps, the screw needs to be a bit skinnier than that really to stop the cable swelling too much

willy



William Revit

That'd be 3/4" long minimum, the longer the screw the better grip it will get, an inch or so would be fine but it does need to be a skinny little fella
William Revit

I have just checked my Pertronix instructions and clearly reading them it is clear to work properly you must have specific resistance in the leads/coil. I couldn’t find it but I am sure I have read somewhere they only work properly with silicon leads. Mine works fine with my light but I have silicon leads and Pertronix Flame Throwe coil.

Good luck

Paul
Paul Dean

Paul (and others) please beware! As Willy has already said, “silicone leads” only refers to the outer insulation. So whether the leads are silicone insulated or old style rubber ones, it’s only the inner conductor core which can have any electrical effect on anything - ie. whether plain low resistance copper or some form of added resistance. So, Paul I really don’t think your comment of “only works with silicone leads” for Pertronix can have any technical basis. Repeating, it’s the type of inner core conductor, and/or resistive or plain plug caps, that can influence performance.
Maybe you meant that anyway and I’m just being pedantic! If so, apologies!
Bruce.
Bruce Mayo

Bruce.
Agreed although going for currently so called 'Silicon Leads' is a safe option for the Ignitor.
According to Pertronixs 'Just avoid any leads with a solid metal core, like solid, copper or steel core leads' so they can be sensitive to HT leads. What is also true is the units are sensitive to the overall resistance of the coil/leads. Personally I will stick with the safe option of Cobalt Silicone leads and Pertronix's coil and everything works including timing light.

Cheers

Paul
Paul Dean

This thread was discussed between 12/11/2020 and 19/11/2020

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