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CB550K3 Plug cap Resistance

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deltarider:
Although I'm open for a possible effect on spark duration - from school I vaguely remember something about Rc time - I doubt a significant benificial effect will be noticed on our bikes.
What I do know, from experience, not only my own but also others' (multiple riders reports): the plugcap has always been the #1 troublemaker on CB500/550s, which for the rest were wonders of reliability. This must have to do with where they are located: not only exposed to oncoming rain and dirt, but, enclosed by the nearby head, also vulnerable to arcing
Right now I'm working on the plugs and caps of mine, so I can share some findings that might interest you. In he past I've run stock coils with NGK 5kΩ plugcaps which seems almost common practice. In the 80s Honda The Netherlands had advised me this. Dyna coils and caps however forced me to fit resistor plugs, as the Dyna caps do not have them.
The other day I bought 4 new NGK DR7EA plugs and I couldn't resist (no pun intended) measuring them. BTW I recommend to always do this, at the counter or - like I did - right after having left the shop. If a plug shows anything odd, at least there can be no discussion. The other two multimeters at home confirmed: 6,1kΩ, 6,2kΩ, 6,5kΩ, 6,6kΩ. Now these are new plugs. Intriguing is that my used DR7EA plugs show much lower values: between 3 and 4kΩ. Where resistance in these NGKs has decreased over time, it has increased in the Denso X24ESR-Us in use. I used to run these in holidays (long distances at high speeds on German Autobahns). These Denso's were new around 5kΩ. When I replaced them, they read: 6,9kΩ, 7,8kΩ, 7,9kΩ and one even 8,5kΩ!
All the above measuring was done on cold plugs. What the resistance will be in the furnace of the combustion chamber? I have no idea.
I have not been able to find any Honda document that is specific on resistance in the secundary circuit. One of the best CB500/550 manuals I have, is the 100 page French one which has been compiled in close cooperation with Honda France. It is also the only manual that mentions something about resistor caps (p.84).
En cas de remplacement, il est important de monter des antiparasites ayant une resistance inferieure à 8000Ω sinon il y a perte de puissance d'allumage.In translation: over 8kΩ, no good.
I'm no expert, but I can calculate. Over 20kΩ in a secundary circuit is a lot. Therefore I personally will not risk reliabilty for a so far only theoretical benificial effect on spark duration. Until proven otherwise, I recommend 5kΩ in either plug or cap, but not in both. But I invite anyone to experiment.
As said, I'm no expert. Here's something I do not understand. If you run no resistance at all, how could that damage the coil?
 

deltarider:
And - please forgive for being such a noob - here's another question. With a dual ouput coil system like ours, what is the consequence for the spark at plug #4, when the #1 sparkplug has sooted so black - let's say due to a carb problem - that it has stopped sparking? Will spark at #4 be compromised and to what degree?

K2-K6:

--- Quote from: deltarider on June 07, 2021, 08:27:07 PM ---And - please forgive for being such a noob - here's another question. With a dual ouput coil system like ours, what is the consequence for the spark at plug #4, when the #1 sparkplug has sooted so black - let's say due to a carb problem - that it has stopped sparking? Will spark at #4 be compromised and to what degree?

--- End quote ---

Sooting doesn't usually stop the plug sparking, it's just not clearing all of the unburnt combustion as it's too cool. Shouldn't affect operation of either cylinder.
You'd have to get the plug properly "fouled" such that it didn't spark before seeing consequences.

My point about resistor plugs and caps is that it doesn't give an observable error (you'd be unlikely to notice any difference if they where to be swapped and you didn't know it) and will not give a fault as such. Honda advise to in Canada market for some of their model.

Interesting topic and maybe worthy of more discussion in dedicated thread outside the OP question.

nairb:
The only thing I can really add to all this is......

I have owned the bike from new and ridden almost all of its 42k miles.  A chunk of that must have been with both plugs and caps having resistance and the bike seemed to work fine.
Its only now after a long restoration/rebuild that I thought to check and change the plugs/caps.  The plugs all checked out at 5k ohms and were probable little used .  The plug caps varied between 5k-12k ohms.

I may not notice any difference with the new parts - except new is usually best for a while.

Interesting info about plugs/caps and resistance tho.

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