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Discussion Starter · #1 ·
Hello all! I am brand new to this forum so please excuse any informalities. I decided to give this a try as I am out of ideas for my bike. I have a 1974 Kawasaki G5 100 that I am trying to get up and running. I have a serious issue though that is stumping me. The magneto on this bike has a couple different wires running out of it that are used to power the ignition coil, charge the battery, lights, horn, etc. Looking at wiring diagrams and shop manuals I have determined that the solid black wire is the one that powers the ignition coil. To eliminate any unseen problems, I have unhooked all kill switches. Essentially, I have the black wire going straight from the magneto to the coil. Now here is the interesting part. The black wire produces spark by itself; that is I have hooked a 12v light up to the black wire off of the magneto and it lights it up. I have also touched the black wire to the bike chassis and it sparks/crackles. However, when I hook the black magneto wire up to the coil, I get zero spark through the spark plug. I have tried three different coils and three different spark plugs all with the same result. I am just lost as to how the magneto wire can produce power when it is hooked up to a test light but not produce spark when it is hooked up to the coil. So I guess my question is what could be the issue and or are there any tests I can run to check the various components of the ignition system? I would like to add in that I have brand new contact breakers (points), a new condenser, and as I said a new coil and spark plug. There isn’t much to this bike and I guess that’s why its getting me so frustrated. If you guys have any tips, tricks, or suggestions I would be more than grateful. I appreciate the help!
 

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Welcome to the forums and thanks for the detailed post.

I have a number of questions and suggestions for you:

First question for you is, what do you mean by "essentially I have the black wire going straight from the magneto to the coil"? Did you totally bypass the ignition switch and kill switch?

Have you checked the ignition coil ground? If this is a frame-grounded coil, then clean up the frame to bare metal and the ignition coil to bare metal. Cover with dielectric grease and reattach. If it is wire grounded, do the same for wherever the ground wire touches the frame.

Did you set the ignition timing when you installed the new points? Did you clean off any packing oil from the points before installation? Contact cleaner does a wonderful job. Final cleaning and drying of the points is done by closing the points on a piece of clean paper and pulling the paper out. Examine the paper for any traces of oil or grease.

Have you checked the resistance of the magneto ignition coil?
 

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Discussion Starter · #3 ·
Thank you for your great response WFO-KZ! I’ll go ahead and answer your questions here:
1. Yes, both the ignition and kill switches are disconnected. I did this to eliminate any possible interference. Right now, the black wire from the magneto goes directly to the coil. There is nothing in between.
2. I just ran out and cleaned the ground for the ignition coil. Scratched the frame down to bare metal and then reinstalled the ground. No luck.
3. I actually just cleaned and gapped the points last night. They are set to 0.3mm-0.5mm.
4. I have checked the resistance. I will state how I did so just so you can make sure I am doing it correctly. I disconnected the black wire (that comes out of the magneto) from the coil, placed one lead from my meter on the end of that wire and the other lead on the stator backing plate, and held the points open with a piece of thin cardboard. I got a consist reading of 0.7-0.8 ohms when I checked last night. I may repeat the procedure today to confirm those readings.

I hope that answers the questions you had. I figured after all this testing I would’ve found something. That’s why I came here to see if you guys could find something I’m missing. Thank you again for the help!
 

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Thanks. You did the test correctly but according to my manual, the readings should be between 1.3 to 1.5 ohms so you are way low. Your coil is internally shorted so it has enough energy to light your test bulb but not enough to run the ignition coil to fire your spark plug.

Are you using a good meter? You may want to try to borrow a better meter if in doubt and run the test again just to be sure.
 

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Discussion Starter · #5 ·
I don’t believe my meter is an issue but I will try another one just to verify the results. Would the test work just the same on a bench? Also, instead of placing a piece of cardboard in between the contact points, could I just disconnect the wire that connects to the points from the condenser?

I do want to ask, could a guy use one of the other two coils on the stator to power the ignition coil? In other words, could I use the lighting coil in the magneto to start the bike?

Thanks again!
 

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I also doubt it is your meter, but worth checking.

The bench test should produce the same results. No harm in disconnecting the points but you will likely get the same result.

Each coil is wound differently, so swapping coils is not an option. If you cannot find a replacement coil you could investigate coil rewinding or conversion to a CDI system.
 

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the charging coils have a different gauge wire and number of windings. How many magnets on the inside of your flywheel? Are they pretty strong? You can unscrew the condenser from from its location and let it hang by its wires instead of disconnecting everything when testing the magneto coil
 

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1973G5100 raises a good point. With age and with impact, permanent magnets in your flywheel will lose strength. In some cases the loss of magnetism will eventually cause such a weak spark, so the bike won't run right or won't run at all.

But in this case we know your magneto coil is bad. Would stronger magnets give you the spark you need without replacing that coil? Maybe.

I would be looking to replace the coil if one can be found, or look into coil rewinding. There is a place that can remagnetize your flywheel if you choose to give that a try.
 

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Did you ever get your bike running? I’m going through the same thing right now, I suspect the primary coil is weak and a new one or rewound one should get my bike running. It’s strange how many Kawasaki 100cc bikes from the 70s have problems with spark
 
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