'78 CB750F spark problems.

Hi guys,

So I recently purchased Dynatek 3ohm coils from DCC along with new spark high-tension copper leads. Set them all up and only get spark from the coil that is plugged into the yellow wire (There's a yellow and black/white wire that attaches to one and a blue and black/white to the other). Whenever I attach the blue and black/white wire to either coil, I get no spark. This rules out the coils and the high tension leads as they both work on the yellow wire. So my next step is probably to check the wires. One thing to note is that there are extra blue and black/white wires that have been attached to the coil almost as an extension. Should I dump those and try to attach the blue wire black/white wire from the harness directly? Please see the pictures for the reference. Let me know if you need more info. I really need your help. Thanks.

Take it slow. According to the wiring diagram I just found, the coils connect to the "spark units" (AKA black boxes). Yellow goes to one box/coil and blue to the other. Black and white is the common power that connects to both coils and to the Spark Units and to the stop switch.

In addition, there are 2 blue leads and 2 yellow leads from the pulse generator to the Spark Units.

Those two leads look like they are the correct ones, but where are the "extra" leads going? And which extra pair of blue and B/W leads are we talking about?


I would check that you have power at both B/W leads.

The "extra" blue lead and black/white lead are the ones I'm holding in the picture. They're not really extra leads but act more like an extension from the coils to the wiring harness. I'm going to buy a multimeter today and try to check the connections.

Those two appear to the the correct connections to that coil. Try connecting the blue lead to the right coil and see if it sparks. If not check the pickups and connection from pickups to spark unit. If that's AOK, then suspect the spark unit.

teazer said:

Those two appear to the the correct connections to that coil. Try connecting the blue lead to the right coil and see if it sparks. If not check the pickups and connection from pickups to spark unit. If that's AOK, then suspect the spark unit.

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Turns out it was the points. I attached the blue and green leads together so they were touching when I put the new ones in. Once I saw my mistake and separated them it all worked flawlessly. Now it turns on and idles superbly! Better than before! Thanks so much for the help.