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OEM Plug Cap Specs

1

1948man

Forum Sage
Past Site Supporter
I've read a lot of threads and am getting mixed signals. I read mostly that OEM and replacement plug caps should have 5K ohms resistance. In this thread, http://www.thegsresources.com/_forum/showthread.php?t=162399&highlight=plug+cap+ohms
The poster refers to an 8.6 ohm resistor in the cap. Also in all cases I have read where someone actually measures the secondary resistance with the plug caps removed, the resistance is always between 12K and 13K. Maybe I missed some threads and maybe it was just a bunch of weak coils measured.
A spare set of coils I have read about 36K secondary for each coil. When I take off the caps, I find that the wire to wire measurement is about 14K for each coil and the caps show about 11K resistance. 14K + 11K + 11K=36K

Is it possible that some OEM caps have higher resistance? Maybe a lot of members who are getting 23K ohm secondary readings with NGK caps on actually have coils that would read 35K if they had the OEM caps instead of NGK 5K ohms caps (6 Ohm loss for each cap).
Maybe my coils are deficient but it seems like a significant coincidence that so many members get fairly low readings with their caps off which would require relatively higher readings for the caps to offset the low wire to wire reading and produce a 35K overall reading.
Or maybe I'm reading in the wrong places.
Any body with a larger, post '80 GS with stock coils and caps feel like taking some secondary measurements with the caps off? I was thinking about ordering one OEM cap to measure it. Thanks Jim M
 
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1948man said:
A spare set of coils I have read about 36K secondary for each coil. When I take off the caps, I find that the wire to wire measurement is about 14K for each coil and the caps show about 11K resistance. 14K + 11K + 11K=36K

Is it possible that some OEM caps have higher resistance?
Click to expand...
It's possible that some OEM caps may be different than 5K ohms, although I haven't seen any that are.

have you taken apart the caps and measured the resistor by its self?
 
Thanks for the reply. No I haven't done that yet. Do you just stick a screwdriver in there and unscrew the piece on the sparkplug end of the cap. I was a little afraid of messing something up but I guess the caps are cheap. I have NGK caps on the bike now and am getting 23K readings with my original coils. I was hoping maybe that low reading is just because the NGK's have less resistance than the OEM's. My bike is running pretty good but only gets 31.5 mpg mixed driving. Maybe that's all I'm going to get with 1100 cc's, pods, and 4 into 1 Vance and Hines. I do like twisting the throttle a little. I have not really figured the mileage for more of trip type setting. Maybe I could get 40mpg or more. I thought I was sooting up #1 plug but realized I didn't have the plug cap pushed down well enough. I had been doing lots of plug chops. The plugs show very little color but are not bone white. I guess weak coils might tend to soot things up a bit?
 
1948man said:
Thanks for the reply. No I haven't done that yet. Do you just stick a screwdriver in there and unscrew the piece on the sparkplug end of the cap.
Click to expand...
Yes... the resistance reading on your coils are about the same as I have been seeing. (around 13K'ish? IIRC)


***edit*** sorry for the short answers. I'm @ work. ;)
 
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Anybody else ever test an OEM plug cap or test the coil secondaries with the plug caps removed? Results?
 
Just checked my coils (with caps) & they're measuring 24k each. That's with brand new 5k NGK caps, so the no-cap impedance should be right around 14k.
 
Just checked my old caps, too. They (only 3; one was found bad last year and replaced with a new non-OEM/non-NGK cap) measured 8.4k, 9.5k, and 10.0k. They're not new of course but there's a really good chance the OEM caps were more than 5k.
 
Thanks Mike and Rusty. It seems a lot of bikes showing 21-25K with NGK 5K caps on have perfectly good coils. Either that or a lot of bikes showing 30-35K with OEM caps on actually have weak coils that are being disguised by caps with higher than original resistance. I suspect it is the first scenario. I'm thinking if you show 20-25K with caps on, you're fine if the caps are only 5K resistance.
 
I'm thinking 20K cap to cap is on the low side and personally I would investigate the coils for shorted turns in the secondary winding. 'IMHO' measurements of 21~25K 'cap to cap' are in the ball park
 
1948man said:
....
....
....
Is it possible that some OEM caps have higher resistance? ..
...
... Jim M
Click to expand...

Ah Ha !
Maybe that is the answer to what I too have been wondering about.
My cap to cap readings have been just under 30K, and factory manaul say more like 35 to 40 K. But I have always had NKG caps (5K each).

.
 
rustybronco said:
I'm thinking 20K cap to cap is on the low side and personally I would investigate the coils for shorted turns in the secondary winding. 'IMHO' measurements of 21~25K 'cap to cap' are in the ball park
Click to expand...

You may be right. I'm not trying to argue for either alternative, just trying to look for the answer and see what others have observed. I will invest in a new OEM cap the next time I make an order. I don't want to pay shipping for one small order. If someone had a new OEM cap to test for resistance, that would answer some questions. Even measuring older OEM caps would give some indications. If there are some older OEM caps measuring 5K, that would mean something.
 
I hate to step into the middle here, but I'm a little confused about the plug caps discussion. In another thread, I thought (perhaps incorrectly, it would seem) that I had determined that I did not need resistor caps on my plug wires. I just ordered the 3ohm Dyna colis to replace the stock ones on my 82 gs650gl. The wires that they had listed were not resistor caps, as far as I could tell. Am I about to screw something up on my end if I install these coils and the aftermarket plug wires?
 
I don't really know. Seems I remember reading that the cap to cap secondary reading on the aftermarket coils was lower so maybe they don't have resistor caps. I'm sure someone will give you a definitive answer. I don't suppose you feel like measuring the resistance of your old stock caps (if you still have them)???
 
I'll be happy to, as soon as I get home from work this evening. To be sure I'm clear, you want the resistance from one plug cap to the other on a OEM coil (non energized, I assume :))
 
Actually need just the resistance of a cap. On a cap removed from a plug wire, just measure from one end to the other. Actually on a whole set of caps if that's convenient.
 
1948man said:
Actually need just the resistance of a cap. On a cap removed from a plug wire, just measure from one end to the other. Actually on a whole set of caps if that's convenient.
Click to expand...


I don't know if these numbers will be useful, but here you are (all in K-ohms):
1)9.3
2)10.14
3)65 !?!
4)14.4

Now, part of my reason for replacing my ignition was that I had a cylinder that wouldn't light reliably that changed when I moved the plug wire to the other cylinder. To be honest, until you asked me to test them, I didn't know you could take them off, so I didn't troubleshoot that far, but that 65K one may well explain my problems.

So the question is: What is it supposed to be? 10? The Dyna's I ordered are the 3ohm green ones, based on what I read in here, but I'm a little worried that these values were all WAY higher than 3.
 
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Thanks, Spadefoot. Just wanted to see if there were any 5K ohm readings floating around on OEM caps. I realize they're old and possibly edging upward but it seems likely OEM caps weren't all 5K ohms.
 
If you took the resistor out and put a piece of metal in its place The bike would still run fine !!
 
Hi,

Here's some specs:

http://www.sudco.com/spark.html

The NGK plug caps come in 1K, 5K, and 10K ohm resistance values.

Depending on the manufacturing tolerance, resistors can vary 1%, 2%, 5%, 10%, etc.

Thank you for your indulgence,

BassCliff
 
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