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correct ignition coils

Submitted by steven_tyrer on Sun, 23/06/2019
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Light Twins

I am soon to start on the electrics on my 1964 Navigator it will be 12 volts and with have Boyer Branson EI, I see that there's a number of options for the ignition coils ranging from the Boyer micro ones to originals coils, the question is which is best?

Steve

Submitted by john_holmes on Mon, 24/06/2019

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Single 12V dual output coil minimum 3 ohms primary resistance or two 6v coils in series each with minimum 1.5 ohms primary resistance (so 3 ohms total). Watch out for just less than 3 ohms, I had a dual coil with a 2.9 ohm resistance, On hot days the Boyer would just stop making a spark after 20 mins, a 10 min rest restored spark for another 20 mins, changed to 2 PVL 6V coils 1.7 ohms resistance and the Boyer has never missed a beat. Original 12V Lucas will give a primary resistance of 3.4 ohms 12v or 1.7 ohms 6V. If you use 2 12V coils then they must be in parallel not series and even then will not give as good a spark as 2 6V in series. 

Do NOT use any coils in parallel (they interfere with one another it does NOT work) unless you use isolation diodes. Adding diodes adds another item to fail (and they do) with a dual output coil you get one good spark but the other spark is less good, (due to electro-thermal effect) as the poorer spark is of reverse polarity and hence not as good. Stick with the 2X6V coils and as it is a Lightweight then the original Wipac coils are recommended, these fit under the tank nicely and the HT outlet hangs down nicely. Yes they are only available second hand but the do seem to last forever. So use the original 6V coils if you have them.

Submitted by anthony_curzon on Mon, 24/06/2019

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Be careful of the Boyer twin coils, as I bought a brand new one from them, and only used it once. The bike would cut out and miss after it got hot. A friend of mine went to Boyer to get his own coil checked and tested, and took my one. They found it was faulty from new. They also admitted that that they get sent back some that are faulty, that they are replaced. My one they refused, as even though they could see it was new, as they said it was too old.

Submitted by anthony_curzon on Tue, 25/06/2019

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After I found out the Boyer twin coil was a dud, I used two Lucas 17M6 6 volt coils and the problem went away, and the bike runs gang buster.

 



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