Topic: Highly suspect a bad ignition coil. Help confirm + advise on replacing one/both

[fizzlebottom]

This is my '82 CB650SC Nighthawk.

Bike started behaving very weird. It would start fine cold, but after ~10 seconds or so it'd behave like it dropped 2 cylinders. After less than a minute, RPMs would pick back up for a bit. It would repeat this cycle til warmed up some more. I could then ride it like normal and everything was fine until the next cold start.

I hadn't ridden in a few weeks at first, so I pulled carbs and cleaned THOROUGHLY. Added fresh gas. No change. All jets are genuine Keihin, same #s as stock, and everything is adjusted by the book.

I suspected something ignition related. Changed spark plugs even though the current ones looked great. All NGK DR8ES-L, by the book. Gapped, etc. No change.

Tested wires with caps on. All tested within spec of ~5k ohms.

Pulled coils and tested resistance of both secondaries & primaries. Both coils' primaries test at 2.4ohms. The secondaries, on the other hand, are worlds apart. One coil is at ~12ohms. The other is flipping between open lead and values in the megaohms range. This test has moved more towards just open lead as it cooled back down after running the bike for a bit.

So do I even need to perform any other tests on that one coil or is that enough to point to it as the culprit.

And if that is the culprit, is there value in just replacing both coils at once?

ADDITION
I am fairly certain that 'good' coil has been replaced in the past. They are both TEC AW82-TRI, but the good one shows a 'D' next to the model and the suspect one shows a 'B'. Usually that goes with a revision.

[xhevi]

I have had plug caps fail on me.

When you do the test try removing the plug caps and test coils and caps separately.

[fizzlebottom]

I have had plug caps fail on me.

When you do the test try removing the plug caps and test coils and caps separately.

Did that. I disconnected everything and tested separately. Caps are all ~5k ohms on their own. The coils were completely off the bike and disconnected from everything when tested.

[HondaMan]

I think you have your 'terms' reversed: the primary side will be about 2.0 to 2.4 ohms on the CB650 coils - depending on who made them. That's the side connected to the 2 little electronic gizmos under the seat.

You can get new coils from PartsNmore: they sell the little electronic modules, too. Take a look here:
https://www.partsnmore.com/parts/honda/cb650/?filters[category]=electrical&filters[fitting]=custom
and their number is #17-6803. They have matching drive modules for it, #14-0504.

[fizzlebottom]

I think you have your 'terms' reversed: the primary side will be about 2.0 to 2.4 ohms on the CB650 coils - depending on who made them. That's the side connected to the 2 little electronic gizmos under the seat.

You can get new coils from PartsNmore: they sell the little electronic modules, too. Take a look here:
https://www.partsnmore.com/parts/honda/cb650/?filters[category]=electrical&filters[fitting]=custom
and their number is #17-6803. They have matching drive modules for it, #14-0504.

Yeah, I think you're right that I have the terms reversed. Fixed in OP.

My ignitors are both good. I replaced them with OE units a few years ago in a fit of "aging parts need to go away" mentality. I have the originals still, so that's not an issue.

Is there any benefit from buying Honda coils vs the universal cheaper units from outfits like Parts N More? Or middle priced ones like Rick's? I've read in more than one place that "coils are coils", but I like build quality when I can get it. Just want some thoughts before I go ordering tonight.

[HondaMan]

I think you have your 'terms' reversed: the primary side will be about 2.0 to 2.4 ohms on the CB650 coils - depending on who made them. That's the side connected to the 2 little electronic gizmos under the seat.

You can get new coils from PartsNmore: they sell the little electronic modules, too. Take a look here:
https://www.partsnmore.com/parts/honda/cb650/?filters[category]=electrical&filters[fitting]=custom
and their number is #17-6803. They have matching drive modules for it, #14-0504.

Yeah, I think you're right that I have the terms reversed. Fixed in OP.

My ignitors are both good. I replaced them with OE units a few years ago in a fit of "aging parts need to go away" mentality. I have the originals still, so that's not an issue.

Is there any benefit from buying Honda coils vs the universal cheaper units from outfits like Parts N More? Or middle priced ones like Rick's? I've read in more than one place that "coils are coils", but I like build quality when I can get it. Just want some thoughts before I go ordering tonight.

I [personally] have the highest 'faith' in Honda's own parts, as compared to anything aftermarket. I've used their parts as first choice for decades (excepting their swingarm bushings) and in all of them, I got just one 750 camchain tensioner roller that was 'bad': I failed to test it before putting it on my shelf, and discovered it bad about 8 months later when I was reassembling that engine. Today, getting Honda's own parts has been hit-and-miss - especially since Covid - but when I can get them, are always my first choice.

That said: there have in the last 10 years been some real good parts showing up. One example of this has been the CruisinImage piston sets, which 12 years ago required careful inspection (and occasional replacement requests) and as late as 5 years ago had cheap rings. This seems to be much better now. There were some really 'fishy' cam chain tensioner rollers from a Chinko knockoff factory, which would seize the poorly-finished bearing and then tore up the roller (PeWe suffered this one himself). The Vesrah gasket sets, once a distant second to Honda's own, are today better than anything else I have found - even Honda's supplied parts (particularly head gaskets), if incomplete with their seals and O-rings. Sometimes I think these parts were omitted from their kits after guys like me railed at them for having the wrong thickness of head pucks (circa 2004-5-6) in the kits, and not increasing the thickness of the oil port head gasket's Orings in their kits while supplying thicker head gaskets: today these parts are simply missing from their kits - a strange response? The other vendors continue to supply the wrong ones, causing many leaky engines for unlucky builders.

I think it's notable that Honda has gone to a lot of trouble to supply (limited-ly) the TEC points and condensors, especially the condensors, for us. It's worth thanking them, because while they are now expensive parts, they are CORRECT parts where the market is otherwise flooded with garbage versions.

[fizzlebottom]

All super good points. I've been sticking with genuine Honda everything as far as I can, except for the nice Ripple Rock Racers / Hindle 4-into-1 exhaust and Progressive rear shocks. That said, I ordered a pair of coils aftermarket from Randakk's. They claim the same resistance as the stock units and I have no reason to try anything different. At a quarter of the price of genuine Honda/TEC units, I won't complain if they give me a few seasons.

[scottly]

The secondaries, on the other hand, are worlds apart. One coil is at ~12ohms. The other is flipping between open lead and values in the megaohms range. This test has moved more towards just open lead as it cooled back down after running the bike for a bit.

So do I even need to perform any other tests on that one coil or is that enough to point to it as the culprit.

Did you try trimming the spark plug wires back a bit, to expose good wire to get a better reading with the meter?
If the coils aren't the problem, the most likely suspects are the pulse generators, or pick-ups. The coils should read about 500 ohms +/-.

[fizzlebottom]

Did you try trimming the spark plug wires back a bit, to expose good wire to get a better reading with the meter?
If the coils aren't the problem, the most likely suspects are the pulse generators, or pick-ups. The coils should read about 500 ohms +/-.

Wires for these coils are removable, so that's how I tested each individual component. Wires and caps tested fine. The 2/3 coil is shot. I ordered 2 new replacements to nip it in the bud.