Author Topic: '76 CB550 spark plug cap resistance  (Read 2394 times)

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Online denward17

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'76 CB550 spark plug cap resistance
« on: June 02, 2024, 07:21:42 AM »
Was checking my spark plug caps to make sure they were within tolerances, I think a couple are way out, but wanted to get your thoughts if I should replace.

Symptoms: Bike runs just a tad rich at low speeds by reading plugs, especially #1.  Carbs have been cleaned and float levels checked and double checked with clear tube test.  All parts in carbs are stock, running stock exhaust, airbox with all new rubber and new air filter.

Tests: (Appear to be original 10K spark plug caps)
#1 cap = 9.8 on 20K scale
#4 cap = 18.9

#2 cap = 13.1
#3 cap = 23.6 on 200K scale

Coils are ok I think,
Wire to wire: 1/4 = 15.3
Wire to wire: 2/3 = 15.2

Thoughts on plug caps?
« Last Edit: June 02, 2024, 07:53:09 AM by denward17 »

Offline HondaMan

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Re: '76 CB550 spark plug cap resistance
« Reply #1 on: June 02, 2024, 09:15:58 AM »
Well, you'll surely have unbalanced spark with those caps. :(
If they happen to be all the same type on your 550 you could squeeze a little more life from them by moving on of each to the other's coil so they would be a little closer in value. They normally should be closer in value on any given coil, lest the lower-resistance side sap away more of the current. They usually will both spark, but after they get unbalanced enough, one plug won't spark well below about 3000 RPM.

Ideally, they should be within 800 ohms of each other. You've got almost a 2:1 ratio on both sides(!).
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Offline Mark1976

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Re: '76 CB550 spark plug cap resistance
« Reply #2 on: June 02, 2024, 06:57:30 PM »
Replace 'em, it's one of the first things I check. Pretty common issue with "old" bikes such as these. Pretty sure you're not going to find any 10 ohm caps anymore, most likely 5 ohm. I continue to run the 5 ohm caps when I can find them, but I still run a points ignition.
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Online denward17

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Re: '76 CB550 spark plug cap resistance
« Reply #3 on: June 02, 2024, 07:15:53 PM »
Having trouble finding a complete set of NGK, not sure if I can get them from Honda yet, most shops are not open until Tuesday.
I know CMSNL has them, but they are $$$.

I suppose I could get some from 4into1, etc, but I think they are China products.

Offline HondaMan

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Re: '76 CB550 spark plug cap resistance
« Reply #4 on: June 02, 2024, 07:26:14 PM »
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

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Online denward17

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Re: '76 CB550 spark plug cap resistance
« Reply #5 on: June 02, 2024, 08:06:11 PM »
I'm seeing ~29 and ~37 for each... ?

Offline Mark1976

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Re: '76 CB550 spark plug cap resistance
« Reply #6 on: June 02, 2024, 08:12:43 PM »
I'm seeing ~29 and ~37 for each... ?
   Look around a bit more, plug caps are getting pricey, I believe ngk's not producing them anymore, but they're out there...
   If you can't find caps, go with a non resistor cap/boot and resistor plugs. 5 ohms is 5 ohms.
« Last Edit: June 02, 2024, 08:24:23 PM by Mark1976 »
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Offline BenelliSEI

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Re: '76 CB550 spark plug cap resistance
« Reply #7 on: June 03, 2024, 05:57:43 AM »
Try this website: clubplug.ca

Based in Quebec, fast shipping, NGK plugs and parts only.

Online denward17

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Re: '76 CB550 spark plug cap resistance
« Reply #8 on: June 03, 2024, 06:11:50 AM »
Placed an order this morning with Yamiya.

Online denward17

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Re: '76 CB550 spark plug cap resistance
« Reply #9 on: June 03, 2024, 06:14:26 AM »
Try this website: clubplug.ca

Based in Quebec, fast shipping, NGK plugs and parts only.

Checked it out, indicates that plug caps are discontinued.....

Offline Deltarider

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Re: '76 CB550 spark plug cap resistance
« Reply #10 on: June 03, 2024, 07:22:13 AM »
I don't know what the meaning of your quest is, but AFAIK the ordinary* NGK ones which all of us in Europe use, are plenty available and they're inexpensive.
*'ordinary' is not the right qualification: they are well designed and very good.
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Online denward17

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Re: '76 CB550 spark plug cap resistance
« Reply #11 on: June 03, 2024, 07:32:36 AM »
I don't know what the meaning of your quest is, but AFAIK the ordinary* NGK ones which all of us in Europe use, are plenty available and they're inexpensive.
*'ordinary' is not the right qualification: they are well designed and very good.

My objective was to find some quality replacements at a reasonable price.  I found a few replacements by some of the US vendors, but not so sure about quality.

Offline RAFster122s

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Re: '76 CB550 spark plug cap resistance
« Reply #12 on: June 03, 2024, 05:43:53 PM »
Delta,try ordering them…beta you are gonna see either old ones show up or a partial order filled with old stock.  The parts distributors in US are exhausted all of the warehoused supply last year for one style, think it is the bent ones that were not available then… now you would be lucky to find them and if you do many sellers cranked prices up to 2-3x the usual price or more…
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Offline Oddjob

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Re: '76 CB550 spark plug cap resistance
« Reply #13 on: June 04, 2024, 07:19:15 AM »
I use red NGK SD05F and NGK XD05F on my 500/550 engine as I find they suit the position really well. I bought mine 18 months ago before the price seemed to rocket up. Now they seem to be double/triple the price I paid.

Quite a lot of fakes out there ATM, I'd avoid using Amazon if I was you.

Online denward17

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Re: '76 CB550 spark plug cap resistance
« Reply #14 on: June 11, 2024, 02:10:34 PM »
Received the new spark plug caps from Yamiya today and got them installed.  Cranked up the bike to make sure it was firing on all 4, seemed to be.

Will take it out in the next day or so.

The new caps are 5K ohms.  With that in mind, should I get the spark plugs that are resistor type?

Assume that Honda wanted a 10K ohm cap and with the new 5K ohm caps, I should change to R type plugs.

Any suggestions?

BTW, the new caps measured from 4.6 to 5.1K ohms.

Offline Oddjob

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Re: '76 CB550 spark plug cap resistance
« Reply #15 on: June 11, 2024, 03:15:48 PM »
The general consensus is that 5k caps, no resistor plugs. Both and it’s too much resistance for the best result.

Not 100% sure but the original caps as fitted from new had no resistance and in the UK they had to be fitted with metal shrouds to stop tv interference as the bike left lines across the tv went it went past anyones house.

Offline bryanj

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Re: '76 CB550 spark plug cap resistance
« Reply #16 on: June 11, 2024, 03:43:15 PM »
I think they all came out of the factory with the shrouds Ken
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Offline Oddjob

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Re: '76 CB550 spark plug cap resistance
« Reply #17 on: June 11, 2024, 06:07:58 PM »
I’ve heard that some markets got different plug caps Bryan, don’t know if that’s true or not but it’s possible I suppose.

Offline Mark1976

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Re: '76 CB550 spark plug cap resistance
« Reply #18 on: June 11, 2024, 07:44:46 PM »
Received the new spark plug caps from Yamiya today and got them installed.  Cranked up the bike to make sure it was firing on all 4, seemed to be.

Will take it out in the next day or so.

The new caps are 5K ohms.  With that in mind, should I get the spark plugs that are resistor type?

Assume that Honda wanted a 10K ohm cap and with the new 5K ohm caps, I should change to R type plugs.

Any suggestions?

BTW, the new caps measured from 4.6 to 5.1K ohms.
   I only run the 5 ohm caps, I always found that the resistor plugs didn't last very long when coupled with the resistor caps. The ohm rating on that cap is going to climb slightly as it ages anyway.
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Offline HondaMan

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Re: '76 CB550 spark plug cap resistance
« Reply #19 on: June 11, 2024, 08:25:27 PM »
The general consensus is that 5k caps, no resistor plugs. Both and it’s too much resistance for the best result.

Not 100% sure but the original caps as fitted from new had no resistance and in the UK they had to be fitted with metal shrouds to stop tv interference as the bike left lines across the tv went it went past anyones house.

Also in rural areas it interfered with car radio (and CB radio) reception.
In the 1972-3 bikes the US models came with 7k caps and the same models in Canada got 10k caps. By the late 750K3 and the CB550K1 they were almost all 10k ohms. We used to get 0 ohm, 5k ohm, 7k ohm and 10k ohm caps all mixed in the shop's inventory. :(
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

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Offline carnivorous chicken

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Re: '76 CB550 spark plug cap resistance
« Reply #20 on: June 11, 2024, 08:40:07 PM »
I'm seeing ~29 and ~37 for each... ?

Just for the record, those are the prices for two.

Offline Little_Phil

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Re: '76 CB550 spark plug cap resistance
« Reply #21 on: June 12, 2024, 03:24:28 AM »
I'm seeing ~29 and ~37 for each... ?

Just for the record, those are the prices for two.
Fraid not, that's each. It just indicates there are 2off each type. Try adding to cart and checking.

I have a set of the meatal shrouded caps that were fitted to the K1. They are 5k ohms.
My very low miles K0 has 7.5k ohms caps and wouldn't be surprised if they are original.
« Last Edit: June 12, 2024, 03:32:14 AM by Little_Phil »

Offline Little_Phil

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Re: '76 CB550 spark plug cap resistance
« Reply #22 on: June 12, 2024, 03:33:16 AM »
I'm seeing ~29 and ~37 for each... ?

Just for the record, those are the prices for two.
Fraid not, that's each. It just indicates there are 2off each type. Try adding to cart and checking.

I have a set of the metal shrouded caps that were fitted to the K1 (at least in Europe). They are 5k ohms.
My very low miles K0 has 7.5k ohms caps and wouldn't be surprised if they are original.

Offline Oddjob

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Re: '76 CB550 spark plug cap resistance
« Reply #23 on: June 12, 2024, 04:07:49 AM »
After looking at a really early CB500K0 parts book, May 1971, it appears that the USA for instance got 30700-300-010 and 30701-300-010 spark plug caps, all pics show them with no shrouds fitted and apparently made by NGK, the UK CB500K1 (we didn't officially get the K0) was fitted with 30700-300-620 and 30700-300-621 and made by Nippon Denso, pics of those show them fitted with the metal shrouds. Whether the resistance of these caps differed is unknown to me, the fitting of the shrouds though does lead me to suspect they were low in resistance and so interfered with radio and TV reception.

I do know first hand though that the metal shrouds caused the cap to overheat and the cap failed as a result, most shops in the UK were removing them even before sale.

I wasn't aware of the market differences until I looked. And yes I know other countries got this or that cap Deltarider, before you chime in, those are just examples to show different markets got different caps.

Another odd thing to note, the early parts books show the caps on the cylinder head page, later books moved them to the kickstart page for some reason.

Offline Deltarider

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Re: '76 CB550 spark plug cap resistance
« Reply #24 on: June 12, 2024, 05:24:05 AM »
The resistor is there to suppress noise, period. We do not know what rules the various markets had. IMO too much weight is attributed to whether caps had: 5, 7 or 10kOhm resistance. There is a risk people will reason that if some models had 10kOhm resistance, Honda must have had a technical reason for it. That's an assumption. Could be, could be not. I have been open for proof for years.
Here's my assumption. Honda wanted their bikes to be legal in whatever markets they went to. This may have led to differences: some markets got good headlamp reflectors, H4, and what not, other markets demanded inferior but always on sealed beam headlights and gadget running lights.
Sometimes markets which themselves did not have specific demands, nonetheless received the same technics one particular market demanded. An example of the latter is the cover over the airfilter case the CB500s for most countries in continental Europe had. Germany had legislation on air intake noise and so Honda needed to fit that cover. Other countries like Holland, Italy, Portugal, Austria didn't have that specific ruling, but got the cover nonetheless. Realise that bikes were produced and shipped in batches. The less different batches, the more economical the production process.
Anyone is free to interprete and connect phenomena in the world around us, but the risk of cognitive dissonans - serving your brain candy - is always there.
If Honda had judged the variety in the resistance of plugcaps technically meaningful, so for other reasons than to apply to local ruling, I personally assume Honda would have communicated on this. Yep, another assumption. ;)


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