Quick single 12v coil ?

Motown1

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Jun 22, 2020
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Gents,

I am planning on doing a 12V single coil conversion on my Commando. I have a Boyer Mark IV with 5 ohm plug wires. I was looking at a 4.5 ohm coil and was wondering if I should still use the resistor plug wires and resistor plugs...BR8ES?

Thanks much.
 
Do the wires actually measure to 5 Ohm at their final lengths? I understood the resistance printed on the sheathing was rated per foot of length.
Would not be concerned with running resistor caps, plugs and wires together on a modern coil. Should have plenty of output for good sparking.
 
I have a 1970s Boyer which fires a double-ended coil and leads from a 1970s CB750 Honda. I have never considered that the leads or plugs I use might be the resistor type. All I know is it works well.
 
Motown1 said:
I am planning on doing a 12V single coil conversion on my Commando. I have a Boyer Mark IV with 5 ohm plug wires. I was looking at a 4.5 ohm coil and was wondering if I should still use the resistor plug wires and resistor plugs...
Click to expand...


The Boyer MkIV doesn't actually need resistor caps, plugs or wires as it isn't a digital ignition.

"Why Do I Need To Use Suppressed Plug Caps?
MKIII and MKIV do not require suppressed plug caps for operation although we recommend using supressed 5000 ohm plug caps. Micro Digital and Micro Power units must be fitted with supressed plug caps. Plug caps fitted with suppression resistors are usually fitted to prevent radio interference. Radio interference (noise) can cause more complex electronic circuits like radios and computers to malfunction.

Our Micro Digital and Micro Power ignition systems contain a small computer operating at high speed that can be adversely affected by radio frequency interference. Symptoms can range from refusal to start to intermittent engine stalling symptoms. Use of non-suppressed plug caps has been known to cause permanent damage to the ignition unit."


Motown1 said:
...BR8ES
Click to expand...

The standard plug for a Commando is BP7ES or resistor is BPR7ES.
 
Your 4.5 ohm (primary circuit) coil sounds suitable.

Your leads can’t be 5 ohm. Do you mean 5 kilo ohm?

It may be bad for performance to have more than 10,000 ohm total suppression resistance in your HT circuit.

So two 5 k ohm resistor plugs, copper HT leads and non-suppressor plug caps would be sensible and easy to get.
 
Thanks for the advice Gents. Yes, I should have said 5k wires. The spark plugs I mentioned seemed to be ok and I have sets laying around the garage so I was using them up. I will try the other plugs you mentioned. Hopefully it works well?
 
Motown1 said:
Thanks for the advice Gents. Yes, I should have said 5k wires. The spark plugs I mentioned seemed to be ok and I have sets laying around the garage so I was using them up. I will try the other plugs you mentioned. Hopefully it works well?
Click to expand...
The "P" is NGK code for "Projected" tip. The the engineers SPECIFIED this type plug for the Commando.
 
Update! A friend offered me a 3ohm dual outlet coil….any issues running this coil with the mark-IV ?
 
Motown1 said:
Update! A friend offered me a 3ohm dual outlet coil….any issues running this coil with the mark-IV ?
Click to expand...
My solution of choice - stock twin lead H-D coils are a dime a dozen around here, and have a primary resistance of 3.5 ohms.

All the H-D owners take them off and replace them with "High Performance" aftermarket ones - seems like a right of passage in H-D ownership...
 
"All the H-D owners take them off and replace them with "High Performance" aftermarket ones - seems like a right of passage in H-D ownership..."

Another in the endless succession of unnecessary parts with highly successful marketing ploys. The only 'upgrade' resulting is the upgrade in the selling company's bank account.

FWIW, I've been using the stock-type dual ignition coils (from Old Britts) in my Commando since '06, when I removed the single coil and Boyer EI that were on the bike when I bought it. They have worked perfectly with the OEM ignition from '06-'08 and then the current Trispark which I installed in '08. To me, along with the Ham Can air filter, the dual coils are major part of the Commando "look." Obviously, that is totally a matter of personal taste and, as Captain Kirk once said, "There's no accounting for taste!" :)
 
MexicoMike said:
"All the H-D owners take them off and replace them with "High Performance" aftermarket ones - seems like a right of passage in H-D ownership..."

Another in the endless succession of unnecessary parts with highly successful marketing ploys. The only 'upgrade' resulting is the upgrade in the selling company's bank account.

FWIW, I've been using the stock-type dual ignition coils (from Old Britts) in my Commando since '06, when I removed the single coil and Boyer EI that were on the bike when I bought it. They have worked perfectly with the OEM ignition from '06-'08 and then the current Trispark which I installed in '08. To me, along with the Ham Can air filter, the dual coils are major part of the Commando "look." Obviously, that is totally a matter of personal taste and, as Captain Kirk once said, "There's no accounting for taste!" :)
Click to expand...
What is more important - form or functionality ? - with two coils there more electrical connectors which can make poor contact. If you have a perfect Commando, you would definitely want originality.
 
L.A.B. said:
The Boyer MkIV doesn't actually need resistor caps, plugs or wires as it isn't a digital ignition.

"Why Do I Need To Use Suppressed Plug Caps?
MKIII and MKIV do not require suppressed plug caps for operation although we recommend using supressed 5000 ohm plug caps. Micro Digital and Micro Power units must be fitted with supressed plug caps. Plug caps fitted with suppression resistors are usually fitted to prevent radio interference. Radio interference (noise) can cause more complex electronic circuits like radios and computers to malfunction.

Our Micro Digital and Micro Power ignition systems contain a small computer operating at high speed that can be adversely affected by radio frequency interference. Symptoms can range from refusal to start to intermittent engine stalling symptoms. Use of non-suppressed plug caps has been known to cause permanent damage to the ignition unit."




The standard plug for a Commando is BP7ES or resistor is BPR7ES.
Click to expand...
Yes LAB but Boyer Brandsen still recommends it and considering the common problems with this ignition personally I would do it.
 
Fanfan26 said:
Yes LAB but Boyer Brandsen still recommends it and considering the common problems with this ignition personally I would do it.
Click to expand...

Yes, "recommends" but only for the reasons stated: "Plug caps fitted with suppression resistors are usually fitted to prevent radio interference. Radio interference (noise) can cause more complex electronic circuits like radios and computers to malfunction." but not required for the ignition itself.
 
Je respecte toujours vos critiques LAB mais Boyer Brandsen dit « pas nécessairement l’allumage » aussi pour moi nous sommes sûrs de rien. Bonsoir Françis ;)
 
Fanfan26 said:
Je respecte toujours vos critiques LAB mais Boyer Brandsen dit « pas nécessairement l’allumage » aussi pour moi nous sommes sûrs de rien. Bonsoir Françis ;)
Click to expand...

The information, however, comes directly from Boyer Bransden and is not a "personal opinion" of my own. ;)
Boyer states clearly that "MKIII and MKIV do not require suppressed plug caps for operation..." nothing translates as: "not necessarily the ignition".

Same for Pazon Sure-Fire as that is also analogue.
"We recommend fitting NGK 5K resistor (suppressor) type plug caps (or
similar good quality make), but you can also fit non-resistor caps."

And Wassell
HT LEADS & SPARK PLUG CAPS
"We recommend fitting a good quality 5k resistor type plug cap
Non-resistor caps can also be fitted."
 
Last edited:
Derek Wilson said:
snipped

All the H-D owners take them off and replace them with "High Performance" aftermarket ones - seems like a right of passage in H-D ownership...
Click to expand...
Yes, because "everyone" knows that you absolutely need a 60,000 volt ignition coil on an engine with a 5,200 RPM redline! :rolleyes:

Quick single 12v coil ?
 
Yep! :) An aftermarket 'high voltage coil does nothing useful on a stock engine. Whatever the manufacturer installed will fire the spark plugs at the spec gap as well as the most powerful coil available.

Of course, a more powerful coil may be necessary on a modified engine...
 
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