Coil resistance/replacement recommendation

Hi all, I've been chasing an electrical (I think) gremlin for a while, where every now and then the revs at idle will drop with a misfire in the LH cylinder, recover and carry on fine (worse with electrical load, disappears if I turn the headlight off). It hates the wet too, running on one cylinder, but not sure if that's linked.

I've just checked the coils. The coil for the LH cylinder showed a primary coil resistance of 5 ohms, which is up on the haynes suggestion of 2.6-3.2. Secondary resistance was bang on.

Visually the coil looks fine, battery is new and well charged, and reg/rec is new. 

Other coil registered perfect resistance.

So question, any recommendations on a replacement coil, and would it be prudent to replace both at the same time? (Or have I done anything wrong in the diagnostics)

Cheers
L

louis_sutton wrote:
I've just checked the coils. The coil for the LH cylinder showed a primary coil resistance of 5 ohms, which is up on the haynes suggestion of 2.6-3.2. Secondary resistance was bang on.

You could go for this one from wemoto:

http://www.wemoto.com/bikes/honda/cb_500_v/97-98/picture/ignition_coil/

'cept I think that is a bit expensive, so looking at ebay:

http://www.ebay.co.uk/itm/New-Ignition-HT-Coil-Honda-CB500-S-93-03-/311208339521?hash=item4875766841:g:qdsAAOSwa-dWos-W

If you fancy taking a punt with 'used' ones then look here:

http://www.ebay.co.uk/itm/Honda-CB500-CB-500-94-Ignition-Coil-Right-/120641268091?hash=item1c16c7a97b:m:mQadD3b4XPFVGD4aMw7spgQ

http://www.ebay.co.uk/itm/Honda-CB500-CB-500-94-Ignition-Coil-Left-/150513727838?hash=item230b51395e:m:mA6HQdnC48tltw1NsTjGHNQ


At the price that I think wemoto want for one then I'd not be replacing both, if I was getting the cheaper one from ebay then I might think about it... mind you, the chance of two of them failing at the same timd is pretty low, so I might just leave the old working one in there and see how long it lasts.

BTW - how do you know it is the left hand cylinder that is misfiring? Is it just the noise?

[size=38]Thanks mate, I'd been eyeballing that one on eBay. I'm a fan of wemoto but I think one off eBay, and if that's rubbish I'll eat humble pie and return to wemoto. I think I'd rather avoid used for the sake of a few quid.[/size]


[size=38]I ran out of time to swap the coils, but two indicators re which cylinder. When wet, the lh cylinder won't start until the engine is spinning nicely, which I took to mean it's generating enough power to overcome the extra resistance and create a spark. If I pull the caps off, it'll carry on running badly with the lh cap pulled, so the rh cylinder struggles on. If I pull the rh cap, it dies.[/size]

louis_sutton wrote:
I ran out of time to swap the coils, but two indicators re which cylinder. When wet, the lh cylinder won't start until the engine is spinning nicely, which I took to mean it's generating enough power to overcome the extra resistance and create a spark. If I pull the caps off, it'll carry on running badly with the lh cap pulled, so the rh cylinder struggles on. If I pull the rh cap, it dies.

That sounds like a very good indication that something to do with the LH ignition is fubar-ed.  Before you go and shell-out on a new coil have you tried replacing the spark-plug on the LH cylinder (just in case)?

I have indeed, I keep a brand new plug around for emergencies. And the gap is spot on too. I do need to check the mixture screw, but the fact that taking electrical load off removes the issue is making me focus on the electrics

I fitted coil on plug or 'stick coils' from a 954 fireblade nearly 50k ago and they work great, no plug caps or leads to mess about with.

Hi Andy, yeah I saw your post. It sounded elegant, and I definitely like the idea. Am I right in thinking it needs the coil loom from the blade as well to use the connectors?

louis_sutton wrote:Hi Andy, yeah I saw your post. It sounded elegant, and I definitely like the idea. Am I right in thinking it needs the coil loom from the blade as well to use the connectors?

You are indeed correct, it does require the loom as well for the connectors. I do have a spare set if you are interested.

Bloody hell Andy, is there abutting you don't have in your garage? Is that a full set of sticks and loom? What do you want for them?

You have PM

Just my thoughts: replace the HT lead(s). Especially the "when wet" part of your story point to these. The leads will degrade with age and are easy (and cheap) to replace. Any car parts shop can supply these.
The small resistance difference may indicate something, but can also be a result of some dirt between the contacts and your measuring probes.

Cheers,
Rob

Thanks Rob. Irritatingly, already done (although the garage that did it seemed happy to find the most likely cause of running on one cylinder at the time, which is why I'm doing it myself this time).

Coil arrived today... I shall report back on any improvement, and if it runs ok, provide the link to the ebay listing for posterity!

Sigh.  Gotta love those previous owners.  God alone knows what coil this was I've just removed.  I take it the routing of the HT lead doesn't really matter?

louis_sutton wrote:Sigh.  Gotta love those previous owners.  God alone knows what coil this was I've just removed.  I take it the routing of the HT lead doesn't really matter?

I don't think it really matters - probably best not to wrap it around the exhaust :)

TBH there is quite a wide variety of coils that would work with the CB500 - not all ones that look the same as the stock one and if you happened to have one lying around... it's just a shame that it has failed!

Did the new coil solve the problem?

Well, it ran with whatever coil it was, so I can't complain.

A quick shake down run suggests it's a bit crisper on the throttle response, starts a touch easier and runs nicely. But the real test will be the ninety minute commune into/across London tomorrow morning, when I shall report back.

Ahs as for the choice of cap head bolt on a coil stashed with chuff all access...

Yep, that's worked a treat, it idles nicely now irrespective of the electrical load.  Very happy.

Not sure ultimately if it was the HT lead or the coil, but since this came with both for£18.50, no complaints from me.  Not as funky as Andy's blade stick coils, but a nice quick and easy fix.

http://www.ebay.co.uk/itm/191583586072?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT