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hay guys thanks for your input lastime out i know its going to help. have a ouestion about difrent volts at batt and coil supply its lower at coil.how do i fix this on 78 kz650 any info is appreciated

id say check your electrical connections would be the first place to start.

If any of the electrical connections(battery cables,connectors,and ground or earth cables) are dirty,loose or have the green crud of corrosion on them, you will have a voltage drop.

some plastic compatible electrical contact cleaner, pipe cleaners from a smoke shop,400-600 grit sandpaper and time to kill should have an improvement in the coil input voltage
ge.

Check the engine stop switch on the right handlebar pod. They get corrosion in there too.

All the above...

And if you still have the symptom and or want the fattest spark then consider the WG Coil Repowering mod. See:

WG Coil Mod

This is how I implemented the Mod. on my KZ650-B1: See:

My Coil Mod

Best of success.

PS
Please add your year, model and location in your signature to get the best responses... and it's considered real friendly too.
Bill

why are you checking this? is it not running correctly or are you just doing some checking??

There is 1 hot yellow/red wire that feeds both coils- completely disconnect that wire and check with your meter to see if you have battery voltage. You probably will see full battery voltage, and you have no problem.

Reconnect to the coils, and you will notice one coil has lower voltage than the other. This is normal, one coil will have its contact points open (no load) the other coil has its contact points closed (loaded). You are seeing a voltage drop because of the loaded coil.

I had the same indication on my bike. Rotate the crank so the points change position, and you will see the voltage drop move to the other coil.

Now, all this is correct provided you have full battery voltage coming out of that yellow/red wire with both coils disconnected from it. If you have a voltage drop at the supply wire with it disconnected from the coils, then you do have resistance somewhere upstream.