Motorcycle Repair: coils, regulator rectifier, voltage spikes

Question
I have a 1979 Kawasaki KZ400. Its a points style ignition I bought it and it had no fire. Put a coil on it and it melted (yeah)it got so hot it oozed. What would be causing that to do that. Would it be the voltage regulator. Maybe? Or any other suggestions would be highly helpful. Thanks

Answer
Hi Shawn,


These are the most likely causes for your bikes problem:

1. Contact points stuck closed, not opening. (bike would not run)
2. Shorted blue points wire. (bike would not run)
3. Faulty condensor. (voltage spikes)
4. Charge rate way too high. (voltage spikes)
5. Incorrect or faulty coil. (Must be 12 volt)
  Primary resistance is 3.2-4.8 ohms between
  the red/yellow and blue coil wires.
6. Shorted battery cell, wrong fuse in circuit.
The fuse will usually blow if too much current flows
to the coils. Check the fuse amperage.

I will break down each one as follows:

When the ignition switch is on there is battery voltage
going to the coil at all times.

The only thing that prevents the coil from
overheating is that the power flow stops
every time the points are open to fire.

When the points break open (.014" gap) on the
highest part of the points cam, a spark
happens.

If the points are very burnt or pitted it might indicate
a poor condensor.

If the ignition is left on without the bike running
the coil will overheat if the points happen to be closed.
This will also burn the points.

Also, the blue wire or the wire that
connects between the coil and the points must be insulated.
If the wire was directly shorted to ground or the bike
frame the coil would burn.

The charging system must keep the voltage
around 14 volts or so.
If it is spiking much over 15 volts that could be
a problem with the regulator/rectifier.

So,
-Use a coil with the correct specs. (12volt)
-Check the blue points wire is not shorting out anywhere.
-If points are pitted badly replace them and the condensor.
-Set points to open .014" on the highest part of the points cam.
-Set ignition timing to fire on timing marks. Move points base
to adjust.
If bike is running good, check charging system.
Connect volt meter to battery and speed the engine up
to 2000-3000 rpm, should be 14 dc volts average.

Use clean battery connections and good battery.
I hope I got the wire colors right or you might
have to translate. ;)

Luck!
Wayne S.
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