Sparking ignition points

[lieutenant dan]

Hey guys. For a while now I've been reading and researching, trying to track down the cause of a misfire on my '79 GS750.

The misfire only starts once the engine gets good and hot. I've read on the forums here about a few guys that had similar issue and it seems the most common suggestion was to replace the condensers. So i went online and ordered a tune up kit (points and condensers: www.ebay.co.uk/itm/392850752997 ).

This evening installed everything from the kit and started the bike up with the cover still off. The bike runs, but I was surprised to see a lot of sparking on both points. I haven't taken it for a test ride yet with the new parts on it because I'm assuming that all those sparks means something isn't right.

Could it be that the new condensers are somehow not grounded? Or maybe the parts i ordered are low quality? Could bad coils or wires be causing sparks at the points?? The points/condensers are the first things I've looked at, so maybe i should move up and check the coils and wires.

Any and all suggestions or recommendations are greatly appreciated! Electronics are not my strong suit, but I'm doing my best to learn how these old bikes work so hopefullyI can get my old girl running a bit better.

[chuck hahn]

Add the bike to your signature please so in the future we dont have to repeatedly ask...thanks. MAYBE theres a service manual here. If not in main menu then click on CLICK HERE FOR MORE MANUALS.

http://members.dslextreme.com/users/bikecliff/

[lieutenant dan]

Add the bike to your signature please so in the future we dont have to repeatedly ask...thanks.

Done! I had said what model and year bike I had in the OP but now I?ve also added it to my signature

[chuck hahn]

sorry....didnt catch it

[chuck hahn]

so choose the EARLY 8 VALVE service manual for the 750.

[Grimly]

If there's more than the tiniest spark appearing across the points when they open, the condensers are shot or not connected right.

[lieutenant dan]

But that?s what I?m not understanding; the condensers are brand new. What are the odds they are both defective out of the box? And I?ve checked and double checked that everything is hooked up correctly - and as far as I can tell it is.

what else could cause sparks jumping across the points??

[Brendan W]

Could you have inadvertantly put a fibre or insulating washer between the condenser lead and the points post?

[lieutenant dan]

Could you have inadvertantly put a fibre or insulating washer between the condenser lead and the points post?

the condensers should be connected to the moving point, same as the wire from the coil - have I got that right?

ive got a photo of how I?ve wired it up, but I can?t figure out how to post it.

[Gorminrider]

yes, sparks at the points doo scream "Condensor".....test for a good ground of the condensor's mount? There should be perfect continuity from it to the frame and the battery "-" post...so you can test that and be sure.

I looked at the ebay listing...I'm grasping at straws -you likely noticed it too, but
"

(((Nippondenso ignition, please check that you have Nippondenso ignition and not the Kokusan, this kit will not replace the Kokusan ignition))).

"

[Grimly]

It's running, and the condensers are doing something, 'cos a knacked condenser causes endless misfires and you have two to do mischief on you.
So, if it's not actually misfiring the condensers are working, but probably not really as well as they should be - aftermarket ignition bits are notoriously unreliable or under-specced, condensers especially.
However, having said that, I distinctly recall many Japanese points-equipped bikes sparking a bit between the points, a lot more than I felt was right, but the engines were running fine. I suspect it's just down to the limitation of size imposed on the design because of where they have to fit, leading to a smaller capacitance than a normal car condenser would be in the same circumstance.
From memory, car condensers range from 1 to 5uF-ish. I don't recall what the Zuk ones are.

[lieutenant dan]

I looked at the ebay listing...I'm grasping at straws -you likely noticed it too, but
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i definitely ordered the correct Nippon ones for my bike. Pretty sure the others wouldn?t fit anyways.

[lieutenant dan]

So, if it's not actually misfiring the condensers are working, but probably not really as well as they should be - aftermarket ignition bits are notoriously unreliable or under-specced, condensers especially.
However, having said that, I distinctly recall many Japanese points-equipped bikes sparking a bit between the points, a lot more than I felt was right, but the engines were running fine.

I guess i'll button it all up and take her for a ride. The whole reason i started into the ignitions bits was cause of a misfire when the engine is hot, so I'd better get the engine good and warm and see if the misfire is still there. If it is, maybe it's time to pull the trigger on one of them fancy Dynatek electronic ignitions.

By the way, here's the photo of how i've got the points and condensers wired. I realize it's hard to see anything, but maybe one of you wise people can spot something i've missed??

[Gorminrider]

That'd be a shame if you don't know what is wrong with the OEM. If you give up and gofor the $$$ solution, you'd want to get ALL new....new coils with new plug-leads+ new plugs as well to be sure you'll have a totally fresh playing field....so, I'd check all these before I gave up and parted with the money. Not because I'm skint but because even more things might be involved. A key switch, or a loose battery connection or perhaps a leaky stator wire? (I've never seen this but it came up in a very similar thread...https://www.thegsresources.com/_foru...id-range-issue) you will be really unhappy if the new stuff doesn't cure it.

It'd really help to identify if ALL cylinders are misfiring or just 1 or 2. These "only when hot" problems can be hard to find but can you warm the bike up in the shop or driveway and look for it then?

[lieutenant dan]

Just a quick update. Despite some arcing at the new points, I closed everything up and took the bike for a test ride. The result; the misfire appears to be gone! It seems likely that the old condensers were the main cause of the misfire that I was getting when the engine got hot.

Strange about the arcing but I guess as one of you said, maybe it’s just normal for these bikes?

Thanks for all the help and suggestions gentlemen!