Topic: Spark arcing from spark plug cap

[papi_sosaa]

Hello everyone, it's been a while. I finished my bike a few months ago and have been trying to take advantage of the short summer weather we get up here in Ontario as much as possible. So far the bikes been running good with minor issues here and there however I have a question regarding the ignition system from the coils to the spark plugs.

Context:
I noticed 2 weeks ago that the spark plug cap for cylinder 4 is arcing through the cap onto the block and is causing a little misfire. I can't tell if it's doing it while I'm riding as the bike seems fine while on the road but I notice and can hear it while it's idling. More specifically, when I'm done riding, petcock is off, and I'm letting it starve itself off.

After taking the cap off cylinder 4, I noticed there was a crack in it. I ordered 2 caps from Vintage750 and replaced them on cylinders 1 and 4 however it's still arcing on cylinder 4, although not as bad as before. I checked the Ohms on the caps and cylinder 1 and 4 were reading about 4.8 to 5k Ohms while cylinder 2 was reading 4.7k Ohms and cylinder 3 was reading 5.3k Ohms. The caps for 2-3 and the wires/coils are original from before my rebuild.

I reused the original wires/caps/coils from before my rebuild as they "just worked" but now with this issue, I want to clean house and start over. I ordered this Ignition coil kit from 4into1 and I'm just curious about resistance.
https://4into1.com/ignition-coils-caps-and-wire-honda-cb650-gl1100-1200/

I'm currently using DR8ES-L spark plugs which I believe are resistor plugs and the caps are resistor caps. I might be misreading the forums as I think I'm getting mixed results but is the total resistance supposed to be 10k Ohms? Should I not be running resistor plugs and caps?

As for Magna/Dyna coils, are those coils only good if you also switch to electronic ignition? Is the benefit just for easier cold starting?

[Deltarider]

[...]
I noticed 2 weeks ago that the spark plug cap for cylinder 4 is arcing through the cap onto the block and is causing a little misfire. I can't tell if it's doing it while I'm riding as the bike seems fine while on the road but I notice and can hear it while it's idling. More specifically, when I'm done riding, petcock is off, and I'm letting it starve itself off.

Why would you do that?

[...] I checked the Ohms on the caps and cylinder 1 and 4 were reading about 4.8 to 5k Ohms while cylinder 2 was reading 4.7k Ohms and cylinder 3 was reading 5.3k Ohms. The caps for 2-3 and the wires/coils are original from before my rebuild.

Readings are within spec.

I reused the original wires/caps/coils from before my rebuild as they "just worked" but now with this issue, I want to clean house and start over. I ordered this Ignition coil kit from 4into1 and I'm just curious about resistance.
https://4into1.com/ignition-coils-caps-and-wire-honda-cb650-gl1100-1200/

That set of coils would also be my choice but... I would have renewed the HT wires.

I'm currently using DR8ES-L spark plugs which I believe are resistor plugs and the caps are resistor caps. I might be misreading the forums as I think I'm getting mixed results but is the total resistance supposed to be 10k Ohms? Should I not be running resistor plugs and caps?

5k Ohm is best.

As for Magna/Dyna coils, are those coils only good if you also switch to electronic ignition? Is the benefit just for easier cold starting?

There will be no benefit. I still regret buying dyna coils. It's a typical American product: all show, low quality. Especially SOHC engines and Dynatek HT silicon wires is not an ideal combination. Those wires are way to supple and will move about in the riding wind and so there's the risk the connection coil - wire or wire - plugcap will be compromised. Also the rubber caps over the connections will become stone hard and very difficult to remove. All in all I am not favouring their connections. Those may work well under a hood. Our bikes have no hood and connections are exposed to the riding wind, SOHC engines more than DOHC. Better have HT wires that are on the stiff side. Your probem with #4 can be solved. Just make sure wire and cap are well cnnected and are not too close to the head.

[MauiK3]

If you replaced the plug cap and there is still "spark leakage" it must be your wires.

[PeWe]

Both my CB750 have used Dynatek 5ohm coils (black) with stock ignition and Dyna-S.
Today, both runs Dyna-S, K6 has Dyna 5 ohm coils.
K2 with stock coils, bought new from DSS, same manufacturer but no Honda bag for a lower price.

Plugs: mostly Denso X24ES-U. I have used NGK D8EA too. D8ES in the 80's
Caps: NGK 5kohm

Wires: I use stiff copper leads. Not too flexible. The harder one sit better in the Dyna coils. The auto connector type can glide out, cyl 1, 4 especially.

[bryanj]

Would help to know what bike you are working on

[scottly]

I'm currently using DR8ES-L spark plugs which I believe are resistor plugs and the caps are resistor caps. I might be misreading the forums as I think I'm getting mixed results but is the total resistance supposed to be 10k Ohms? Should I not be running resistor plugs and caps?

If you are running resistor caps, you don't need resistor plugs.
Try running the bike in the dark and look for any arcing.

[papi_sosaa]

I'm currently using DR8ES-L spark plugs which I believe are resistor plugs and the caps are resistor caps. I might be misreading the forums as I think I'm getting mixed results but is the total resistance supposed to be 10k Ohms? Should I not be running resistor plugs and caps?

If you are running resistor caps, you don't need resistor plugs.
Try running the bike in the dark and look for any arcing.

Does the bike not come stock with resistor plugs and caps? Would the bike run that much better if you only used one or the other? i.e. Resistor caps but normal plugs vs. normal caps vs resistor plugs?

Would help to know what bike you are working on

1982 Honda CB650SC Nighthawk

[papi_sosaa]

[...]
I noticed 2 weeks ago that the spark plug cap for cylinder 4 is arcing through the cap onto the block and is causing a little misfire. I can't tell if it's doing it while I'm riding as the bike seems fine while on the road but I notice and can hear it while it's idling. More specifically, when I'm done riding, petcock is off, and I'm letting it starve itself off.

Why would you do that?

I figured I was doing the carbs good by trying to keep the bowls empty.

I reused the original wires/caps/coils from before my rebuild as they "just worked" but now with this issue, I want to clean house and start over. I ordered this Ignition coil kit from 4into1 and I'm just curious about resistance.
https://4into1.com/ignition-coils-caps-and-wire-honda-cb650-gl1100-1200/

That set of coils would also be my choice but... I would have renewed the HT wires.

HT wires? Is the wire in this kit not good?

[rotortiller]

Check the spark plug gap, maybe swap plugs and try some dielectric grease on the cap boots and the wire entering the cap. New coils with wires are cheap.

[dave500]

put new non resistor plugs in.

[bryanj]

The 650 runs a totally different ignition system from the earlier 500/550/750 and is known to have problems with igniter units after many years.
You need to check in a proper Honda manual for the correct ohms reading for original coils and stick to it, i do not have that manual to check for you.

You should be able to replace leads and caps to stop arcing

[scottly]

According to a Clymer manual for the 1979-1982 DOHC 750, the US models used non-resistor plugs, but the Canadian models used resistor plugs.
Are you sure it's really arcing, or are you hearing a tick from something else, like an exhaust leak?

[papi_sosaa]

The 650 runs a totally different ignition system from the earlier 500/550/750 and is known to have problems with igniter units after many years.
You need to check in a proper Honda manual for the correct ohms reading for original coils and stick to it, i do not have that manual to check for you.

You should be able to replace leads and caps to stop arcing

Checked my Clymer manual and I see Ohm values for the coil pickups but nothing for the coils themselves.

According to a Clymer manual for the 1979-1982 DOHC 750, the US models used non-resistor plugs, but the Canadian models used resistor plugs.
Are you sure it's really arcing, or are you hearing a tick from something else, like an exhaust leak?

100% it's arcing from the plug cap.

Based on my clymer manual, the 1979-1981 US models don't need a resistor plug but it says the Canadian models do. For 1982, they just say the standard plug is a resistor plug, no country model variance.

Is there a big difference between the 1981 and 1982 models? Why the change for plugs?

[scottly]

Have you inspected the plug itself yet? Is the gap too large? Maybe the resistor in the plug has gone open?

[scottly]

Is the arc coming from under the edge of the rubber boot?

[papi_sosaa]

Have you inspected the plug itself yet? Is the gap too large? Maybe the resistor in the plug has gone open?

I looked at plugs 1 and 4 and they look good, both showing signs that the engine is combusting properly. Gap on plug 4 is 0.28 which is on the higher limit for this engine, which the book says should be between 0.24-0.28.

Is the arc coming from under the edge of the rubber boot?

Looks like it's arcing near the middle, just above what I guess you'd call the sleeve or boot on the bottom of the cap where it connects to the spark plug.

[scottly]

Is the boot on the bottom new? If yes, replace the spark plug.

[papi_sosaa]

Is the boot on the bottom new? If yes, replace the spark plug.

I initially noticed the arc on cylinder 4, inspected the cap and saw that there was a hole in it. Replaced the caps on 1 and 4 but it is still arcing on cylinder 4. That picture of the arcing from my previous message is of the new cap. Both caps came with new boots already on them.

I don't see anything in the book about resistor caps. Should you be running both resistor caps and resistor plugs?

[scottly]

It's not the resistance of the secondary circuit that's causing the arcing: the resistance is only for radio noise suppression. Besides, the other 3 cylinders don't have the same problem.
Is the porcelain cracked on that plug?

[papi_sosaa]

It's not the resistance of the secondary circuit that's causing the arcing: the resistance is only for radio noise suppression. Besides, the other 3 cylinders don't have the same problem.
Is the porcelain cracked on that plug?

I'll double check again tomorrow but it didn't look damaged when I was checking the gap.

[scottly]

Replace the plug in any case. BTW, did the hole in the old cap look like it had burned through from the arcing, and was it in the same location as the arcing now?

[papi_sosaa]

Replace the plug in any case. BTW, did the hole in the old cap look like it had burned through from the arcing, and was it in the same location as the arcing now?

I'll run over to my parts store tomorrow and grab some new plugs.

I believe the arcing is in the same place however the old cap looks like it got chipped rather than burned.

[scottly]

I would guess that the chip might be related to a broken porcelain??

[Deltarider]

[...]

[...] I ordered this Ignition coil kit from 4into1 and I'm just curious about resistance.
https://4into1.com/ignition-coils-caps-and-wire-honda-cb650-gl1100-1200/

That set of coils would also be my choice.

As a matter of fact: that set looks ideal also for CB Fours with conventional breakerpoints ignition. Just add a 2 Ohm ballast resistor in the primary route. I favour screw on connections like these coils have. I can't comment on the quality of these particular coils though.

[dave500]

Replace the plug in any case. BTW, did the hole in the old cap look like it had burned through from the arcing, and was it in the same location as the arcing now?

I'll run over to my parts store tomorrow and grab some new plugs.

I believe the arcing is in the same place however the old cap looks like it got chipped rather than burned.

well that cap is #$%*ed for a start.