5k ohm or 10k ohm plug caps

[Guest]

I need to order new plug caps for my '79 GS850. The OE-looking caps I have measure 10k ohms resistance but I see that 5k ohm seem to be most popular on this forum and more plentiful on EBay. VB05F and XB05F are what is a good match to OE.

Would there be a problem going with 5k ohm? Does the fact that my GS has points ignition make a difference?

Thanks in advance.
Brian

[Steve]

Just because your current caps measure 10k does not mean that is correct.

Actually, I have done absolutely NO research on the topic, but I have only heard of 5k caps, so assumed that's what was available.

Looking at the manual for my 850, there is a specification for the secondary side of the coil of 15kΩ. Later, in the supplement for the '80 850, it gives a specification for plug cap to plug cap of 31-33kΩ. If the coils were the same (and they are not), that would hint that the resistance of the caps would be about 8500Ω each.

As for your points making a difference, you should be more worried about the primary side resistance, which should be about 4Ω. The resistance of the wires and/or caps on the secondary side is mainly for noise suppression, to not disturb the radios in the vehicles near you. A lower resistance might mean a bit more noise in someone's radio, but it will be a stronger spark at your plugs.

.

[canuckxxx]

Thanks for the response.

Now that I have the plug wires removed from the one coil I measured the resistance of just the coil and get about 11k ohms. The one lead that I cut off that I think is OK measures about 10k ohms, the other which I think is shot measures 3m ohms. The other coil and leads that are still all together measures about 33k ohm from cap to cap. So about 10k ohms for each plug wire and cap. I also unscrewed that brass thing from the cap and took the resistor out and measured about 10k ohms.

Gold standard would be to hear from someone who has used the 5k caps on a '79 GS850. Having said that I can't see any reason why the 5k caps wouldn't work on my bike.

[Steve]

Again, I have only ever heard of the 5kΩ caps being used, and have heard nothing negative about them.

Also, it is recommended that there is some suppression somewhere in the system. This can be achieved by using suppressor wires, suppressor caps or suppressor plugs. Any ONE of them would do the job, but only one is necessary.

.

[Gorminrider]

Well...there's always the interweb thing: a quote from NGK "Combined usage of the resistor covers and resistor spark plugs is more efficient to suppress ignition noise from engines in motorcycles, snowmobiles, farm tractors and so on."
(http://www.ngksparkplugs.ca/products...s-and-caps.cfm)

So, I would take from this that , replacing them with your easier choice

more plentiful on EBay

- 5k ohm resistor cap (NGK XB05FP) is fine if you also add a pair of BR8ES (5k ohm) resistor type. That combo nicely replaces the original 10k caps since your original plugs are NOT resistor plugs

But whichever, the air gap of the plug has way more "resistance" than any of the above unless it gets choked with carbon

[Redman]

QUOTE///////////
VB05F and XB05F are what is a good match to OE.
////////////ENDQUOTE

THose are what I was going to suggest.
And also say the caps are 5K, but as they age from use and heat they go to higher resistance untill are almost an open circuit. I found one at almost 20k by itself.
Typical is cap to cap ohm reading is 30K, which is 5K for each cap and then about 20k for wire to wire (including the coil).

A 79 850, stock, will have points, and a different coil than 80 and after (electronic signal generator). I think it is the low voltage side of the coil that is different, and the high voltage side is the same.
ANyway, like Steve said, and you have found, most all the caps are 5K. And that is what you need.

[limeex2]

So would 5k caps along with BR8ES, or in the case of a 4v motor, DR8EA be the way to go with pointless type ignitions? Both specify non-resistor type plugs. Would Dyna coils make a difference in either caps or plugs?

[limeex2]

So would 5k (VB05F and XB05F) caps along with BR8ES, or in the case of a 4v motor, DR8EA be the way to go with pointless type ignitions? Both specify non-resistor type plugs. Would Dyna coils make a difference in either caps or plugs?

[1978GS750E]

Check our sparkplugs.com for your caps. Cheapest price that I have found and excellent delivery time!

[LAB3]

Rather than over thinking every possibility it might make more sense to find a seller with an application chart and choose the one specified for your bike.

[Steve]

So would 5k caps along with BR8ES, or in the case of a 4v motor, DR8EA be the way to go with pointless type ignitions? Both specify non-resistor type plugs. Would Dyna coils make a difference in either caps or plugs?

Well, you can follow along with the hundreds of us that have installed Dyna (green, 3Ω) coils, solid wires, NGK 5kΩ resistor caps and B8ES (or D8EA) plugs, or you can blaze your own trail.

Let us know how it turns out.

.

[canuckxxx]

OK, 5k caps on order.

[Cipher]

I seem to recall my bikes oem caps being higher than 5k ohms
but I have the ngk 5 k ohm caps and run with zero problems

Although if I pass the ;last CB radio guy left alive I may be momentarily messing up his reception.

There was an interesting article and flame war on a Honda forum years back. Engineer types hating on each other over a similar problem.

Apparently the resistance is a factor in how fast the spark intensifies and disipates. A single instance is fast to humans but to air fuel mixtures and different compression ratios its a huge thing
sort of

[Gorminrider]

Apparently the resistance is a factor in how fast the spark intensifies and disipates.

and that's why I would incline to stay with a sum of 10k...
....I'm making this up,so there's lots of "..." but the "issues" of RF and "reluctance" would seem to be about the coil's disharge creating a magnetic field that expands and collapses along the plain-wire plug lead....the spark itself is in the engine and is not much "rf" because it's muffled by the engine block...anyways, when it collapses, it creates a current on the lead back into the coil that retards the coil re-energizing... it might explain a certain amount of controversy especially at higher rpm....
That said, and maybe I have it backwards? because various manuals I have mention NON-resistance plugs allowable as substitutes "at highway speeds" so perhaps that's offered because the backwash effect is lessened when the coil never has a chance to fully recharge anyways? oh well.

Still, a sum of 10k ohm at the cap alone or cap+plug is electrically the same thing except the nature of the plug's resistance removes it from the length of the "antenna" which I underlined because I think it's a pretty cool idea, not because I know it's important.

[roeme]

Meh, NGK says resistor vs. no-resistor has at best a minuscule effect on engine performance: http://www.ngk-sparkplugs.jp/english...q08/index.html

Personally, I prefer no-resistor caps (less stuff that can go bad in them, methinks) with resistor spark plugs – but depending on parts availability, I don't mind the other way round as well, or no resistors at all. (AM radio has long since gone the way of the dodo, and CB never picked up much around here). In any case, just don't combine both with integrated resistors.

I've got an old ignition scope in storage, some day I'll get around to scoping out the difference between the combinations.