No spark on ignition coil connected to the blue wire

[Siloxious]

Hello everyone!

As I'm restoring my CB 500 Four K1 - General Export, I've ran into a problem with the ignition. The spark plugs connected to one of the two coils don't give spark (the coil connected to the blue wire).

I know the problem isn't the ignition coil, it's HT leads and spark plug caps, because I've recently bought new ones and when I switch the blue and yellow wires of the coils, the one that was faulty before now gives spark and the other one doesn't anymore.

The problem can also not be due to bad wires.
I've checked the connection between the blue wire and the ground and they are connected on the right time of the ignition cycle.
I've also switched the wire that gives power to the coils (the black - white wire) and it still doesn't work.

The problem is also not related to faulty spark plugs. They're brand knew and if I switch them, the problem isn't resolved.

Does anyone have any experience with this kind of problem or have a suggestion where I can look for the problem?


Thanks in advance!

You can find the wiring diagram down below (the bike is wired like a K3).

[Johnwebley]

Check the contact points are assembled correctly, and not just earthing,




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[Oddjob]

Have you tried swapping the condensers over?

How did you check the blue wire? they are known for having bad connections in the bullet connectors near the rear brake light switch, I'd check that.

It's something simple that you just haven't spotted yet.

[robvangulik]

Check the contact points are assembled correctly, and not just earthing,

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This. If the insulating rings aren't in the correct order on the points screws they're constantly earthed.

[Oddjob]

Check the contact points are assembled correctly, and not just earthing,

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This. If the insulating rings aren't in the correct order on the points screws they're constantly earthed.

Reading what he said about the points earthing when they should at the right point of the ignition cycle means they can't be permanently earthed, it was my first thought as well. However that test would depend on where he was testing the blue wire from, if he's tested it at the bullet connector near the brake light switch then it's possible the lead is earthing higher up, maybe worn on the frame etc. Simple test would be to disconnect the blue wire entirely and run a wire from the coil down to the points and see if it fires then. If it doesn't it's looking like a faulty coil, however swapping the coils doesn't seem to lead to this conclusion, it has to be the wiring IMO.

[Seabeowner]

Simply, the black/white wire supplies the +ve volts to the two coils. The blue and the yellow wires from the coils go off to the points. (there is a bullet joint connection down the RHS) The points earth the volts, and therefore allow current through the coil to the engine when they are closed.
If you remove the connection to the points and dab the wire to the engine, you should get a spark as you remove the dab. (just like the points opening)

[Siloxious]

Hi everyone

I’ve swapped the condensors and there’s now spark on all four cilinders. I think the problem was a bad connection of one condensor to the blue wire.

Thanks for the help!