Converting NGK resistor caps to non-resistor. NOT!

Mike G

Mike G

Mike G
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FWIW, I’ve seen a lot of discussion lately on NGK discontinuing the non-resistor spark plugs we use and having to change plug caps to the non-resistor type to be able to use resistor plugs. I recalled seeing somewhere that the internal resistors were removable/replaceable. A quick search found many examples on how to do this, it’s very easy and better yet free. Rather than scour the globe for the remaining non-resistor plugs when the time comes, I plan to convert the plug caps to non-resistor and use the readily available resistor plugs going forward.
 
Don't want to usurp this thread, but I'm confused over the use of resistor plugs on bikes. I think most xs650s originally used non-resistor plugs. Does that mean the original factory plug caps were resistor caps? Why use a resistor plug or cap on a bike when RFI isn't typically an issue?
 
NP2650 said:
Don't want to usurp this thread, but I'm confused over the use of resistor plugs on bikes. I think most xs650s originally used non-resistor plugs. Does that mean the original factory plug caps were resistor caps? Why use a resistor plug or cap on a bike when RFI isn't typically an issue?
Click to expand...
I believe I read somewhere that 5 k resistance would give a better spark, as the energy discharge was sort of "held back" by the resistance, and then jumped the plug gap with higher energy.
 
WideAWAKE said:
Just get a non resistor plug cap.

Simple.
Click to expand...

Simple, yes, makes sense, yes, but let me see, how do I put this delicately...I'm CHEAP!

If it costs me a few minutes and a small piece of wire then I'm happy.

Just wanted to offer fellow members another alternative in the impending global non-resistor plug crisis.
 
NP2650 said:
Don't want to usurp this thread, but I'm confused over the use of resistor plugs on bikes. I think most xs650s originally used non-resistor plugs. Does that mean the original factory plug caps were resistor caps? Why use a resistor plug or cap on a bike when RFI isn't typically an issue?
Click to expand...
Yes OEM caps have 5K resistance.
The ignition circuits are not simple as they appear. IMHO unless you've really dug into the theory and spent some time with a scope analyzing secondary spark wave forms before and after changes, best stick with what the engineers designed. IE 5K of resistance in the secondary. Your choice; spark plug or plug cap.

You want Beaker Street to be loud and clear when late night cruising!
If you get that last line you're a fossil.
For the rest of you; https://www.tigerdroppings.com/rant...le-rock-in-the-late-60s---early-70s/54505197/

 
Last edited:
From the factory XS650 J-K service manual;
KIMG4359~2.JPG

Cap 5K +- 20%
So far none of the earlier service manuals I have mention a spark plug cap spec.
 
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Agreed. I don't think we will find printed confirmation of what the points bikes used.
I searched this forum for "9K cap", and got many 5twins hits, but none from anyone else.
I searched the old "Garage" forum, and found more 5twins posts and a post from Curly (of charging system trouble-shooting fame):
https://xs650temp.proboards.com/thread/8031/coils
second post.
If you search Google for "9K cap", you get lots of Honda hits. Apparently Hondas of the era used 9K.
I'm sticking with the theory that 9K caps were used with points, and 5K with TCI.
 
SOME resistance is a good thing, helps insure a clean strong spark, :twocents: but I don't think the exact value is critical, ie somewhere between 4K and 12K in either the spark plug OR the plug cap will be fine. A few here have reported no problem running both a 5K cap AND a 5K plug. But I don't think I'd do that as a normal practice. :shrug:
There are some significant differences in firing a coil with a points system vs an electronic system. Mostly having to do with amount of coil primary saturation over varying RPM, the electronic system can compensate to achieve best spark while avoiding coil overheating in ways a points system can't.

A quote from; https://www.onallcylinders.com/2022...y-in-your-ignition-systems-spark-plugs-boots/
"But as anyone who works around old electronics already knows, resistors can drift off-spec with age. In my experience, it often means the resistor will gradually increase its resistance, until it ultimately fails open and you get a complete break in continuity. (In fact, we saw this with an old blower motor resistor a little while ago.)"
If you're interested, that's a relevant article.
This; https://www.motor.com/magazinepdfs/052001_04.pdf goes into more depth and perhaps illustrates how complex this can be.
Short version? low resistance: long low voltage spark, high resistance: short high voltage spark.
Somewhere in the middle will suit most normal operation. It also hints at problems that random ignition hotrod parts can cause, looking at you (Mike's green monster coils), LOL
Another article hints that spark plug gaps much outside .028" to .040" can cause weird problems also.
 
Guess I should have looked at my caps before posting.

The LB05F and LB05FP caps that I have DO NOT have the screwdriver slot (nor any other hex/flat/etc. feature) shown on all the videos/posts I found online so guess I will be buying non-resistor caps after all. Such is life...

As the "church lady" used to say..."Never mind!"
 
I only know about the 9K Ω caps from measuring them, I never found it listed anywhere. The '78-'81 Service Data charts have the caps listed as 10K Ω, in '82 it changes to 5K Ω. When I was putting my '78 together many years ago, I had a pile of used coils and caps. I checked through them to find some good ones to use. I did, but I also discovered some bad coils and caps in the process. The caps had resistance values of like 12K to 15K Ω, clearly bad. The good caps were all in the 8 to 9K Ω range. While running the points ignition, eventually I eliminated the resistance caps altogether and ran zero ohm caps. It ran fine like that, maybe a bit better, but certainly no worse than with the resistor caps.
 
5twins said:
I only know about the 9K Ω caps from measuring them, I never found it listed anywhere. The '78-'81 Service Data charts have the caps listed as 10K Ω, in '82 it changes to 5K Ω. When I was putting my '78 together many years ago, I had a pile of used coils and caps. I checked through them to find some good ones to use. I did, but I also discovered some bad coils and caps in the process. The caps had resistance values of like 12K to 15K Ω, clearly bad. The good caps were all in the 8 to 9K Ω range. While running the points ignition, eventually I eliminated the resistance caps altogether and ran zero ohm caps. It ran fine like that, maybe a bit better, but certainly no worse than with the resistor caps.
Click to expand...
My experience checking through boxes of used caps are exactly like above, except my "good" caps were in the 9-11K range, which Curly supported.
And I also used to run points with no resistance at all, an idea that Pamco Pete repeatedly said was okay. He used to buy and use Volkswagen wire sets, the ones with the caps attached.
I still have some of these:
https://www.oreillyauto.com/detail/...-super-stock-spark-plug-wire-set/acc7/3009acc
which is what I bought instead of the Volkswagen ones. The price is up, but still not a terrible deal for a plug/wire combo.
And, I will continue to use them. I've gone back to points on the 70-79 models, after very bad experiences with XS Charge and Tytronics ignitions. Honestly, can't someone else make the original Pamco now that Pete has retired?
 
You made me look, out to the SOIR with a VOM
used caps
caps still on a complete points, wiring harness, coils, even B8EA plugs..
used caps, 9K, 10K, 7.5K, 11K
tossed out 2 caps that read infinity.
Caps still attached to TCI coil wires
9K, 5K (a deep maroon color)
2 new black caps in a bag 5.5K, 5K
Accel coil wires with caps about 16" long; 12K, 15K
Accel 140403 yellow coil secondary 12K
Some used points coils, secondary circuit; 11K, 11K
Used TCI coils secondary circuits, plug wire to plug wire; 11K, 12K, 12K
2 "new" mikes'XS coils secondary circuits, 15K primary 2.5 ohms
2 new coil wires in a bag .2 ohm, a used stock coil wire about 1 ohm.
All for now.
 
Comedic interlude to follow.......
I changed my stock caps out to NGK's that accept plugs with the full rounded contact so I could run an Autolight 64 in the right cylinder and a 65 in the left......some voodoo magic about trying to even out the generated heat difference between cylinders. Dunno, bike runs great and plugs are readily available. OK, that's one diversion away from the Japanese engineers design, I'll admit, but hey! I talk to crows, make deals with coyotes and play with snakes.
Carry on....
 

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