Z750 (B) 1977: Ignition coil won't draw current? - There's voltage

Hello everybody,

I'm brand new to the forum as a member but have used the information on this forum many times already during the restoration of my Kawasaki Z750B from the year 1977.

I truly did a 'nut and bolt' restoration of the motorcycle: everything was taken off and freshened up. I let a company powder coat the frame as well. I had no prior mechanical knowledge so I am using this forum, YouTube and the workshop/maintenance manual of the bike. I did not touch the engine as it worked perfectly before it stood still for 20 years in a dry storage room.

After everything was bolted on, the motorcycle engine turned on and sounded great: it shifted great and the brakes were great as well.

I am currently stuck however: I have an issue with my ignition:

When I turned the ignition on and then put the switch on the right handlebar to 'on' (the kill switch), I would see that the Neutral light on the dash (as well as the headlight, I think) would dim a bit. I think this is because the ignition coil is absorbing energy.

One day, I turned the kill switch to 'on' and then the lights on the dash would dim a bit and then shine normal again (and then dim a bit again) : so it was dimming intermittently until it just stopped dimming after a few seconds. Now it is not dimming anymore and I cannot get a spark (read: fire up the engine). It's strange because I had the impression that it would dim continuously when putting axial pressure on the kill switch (in direction of the handlebar) but now this is not working: the lights do not dim anymore. I already took apart the switch and restored it back togheter - it looks okay. I measured the voltage at the ignition coil with the kill switch on (and no lights dimming on the dash of-course) and I measured half a voltage less than when measuring at the battery directly. (I think this is normal?)
I tested the primary resistance of the coil and that was just fine: 3.2 Ohm. I can't remember if I pulled it out to measure the secondary resitance a while back but I think I did and it was fine. (The bike has been standing still for a few months now - I just can't find the issue...)

An even stranger thing happened when I found the time to look at the bike again last week and the light on the dash would dim a bit for a while with the kill switch set to 'on' however after giving the kickstarter a kick, it was gone again.

Does anybody have advice on what could be the cause of this strange issue? I could not find a previous topic with this exact same issue so I am hoping that someone of you people can help me! Thank you in advance!


 

It could be a lot of things.
Probably best to do a quick check the state of your electrical system.

Grab your meter
Set to DC V
Leave all electrical connectors connected during these tests unless told to disconnect them.

Key switch set to ON
Kill switch set to RUN

Red probe on positive battery post(post is the metal part of the battery)
Black probe on negative battery post
note voltage to the nearest tenth place(example 12.6V)

Move your red probe to the fuse box
measure each side of all the fuses(this will give you two readings per fuse)
Note voltages

Turn off bike

Hello,

Thank you for your response!

I did as you proposed: I measured the voltage of the battery: 12.1V

I measered the voltages at the fuses (both sides):
Left fuse: 11.7V
Middle fuse: no fixed value but it's in mV so there's no power here
Right fuse: 12.1V

So the middle fuse (both sides have a blue wire) is not getting any power. I followed the blue cable to the resistor and there was also no power here.

I looked at the wiring diagram and it's logical that there's no power to the resistor. I am however not capable of interpreting the wire diagram past this point.

What should I be looking for? What are the appropriate next steps?

Thank you in advance!!


PS: I apologize for my lack of knowledge on this matter

 

I fixed your pictures for you to be seen full size. Next time click the insert all tab to complete the installation
 

Your blue wire is your headlight circuit..
You actually need to follow the other wire on the fuse.. it will be blue wire with a white stripe. It goes to the right handlebar on/off switch(could be a headlight switch). That is where the power is coming .
On the right handlebar it looks like you have a headlight on/off, a engine kill switch, and a starter button.

Your key switch appears to be working ok excpet for the blue wire voltage, but that may be the headlight switch is in the off position or a bad connection.

I'll sit down in a couple of hours and write up some more tests.


Actually, there is one wire that can cause serious headaches.
It's the black wire with yellow stripe coming off of the batteries negative terminal.

Key switch on
Kill switch Run
meter DC V

red probe on positive battery post
black probe on black\yellow wire coming off the battery.
You'll have to keep the connector connected..slip the probe under the terminal boot for that wire.

You should have close to battery voltage.
Any reading 0.5v lower than battery voltage could be an issue.

Move the black probe to a metal part of the cylinder head.
Reading should be close to battery voltage as well

Turn off bike.

one other thing..
make a list of things not working and things that do work.
I'll make the list---tell me if these items work or don't work
right front and rear turn signal
left front rear turn signals
tail light
brake light front
brake light rear
horn
headlight high/low
tachometer light
speedometer light
oil pressure warning light
neutral light
high beam light
starter

 

 

These symptoms would suggest a partial short to ground between the kill switch and coil (check if there is continuity between the +terminal of the coil (with the wires disconnected) and the mounting post of the coil, this should be "open circuit" as there should be no internal connection to the core)

A weak battery or bad/oxidised plug/switch connections are most favorite voltage drop trouble maker !!!
Sometimes self de-soldering glas fuses due to permanent max current limit use are also possible hidden gremlins.

Scirocco wrote:

A weak battery or bad/oxidised plug/switch connections are most favorite voltage drop trouble maker !!!
Sometimes self de-soldering glas fuses due to permanent max current limit use are also possible hidden gremlins.

Possible but I would expect a resistance fault to cause a "Volt drop" after the resistance in the kill switch not pull the whole circuit down (unless the resistance is much further back (ign switch, fuse holder etc and the additional load of the coil is causing the drop off across the circuit)
A quick test would be to disconnect the coil and see if the fault is still apparent when the kill switch is operated