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Discussion Starter · #1 ·
I work on a lot of old bikes and developed this trick.

Your battery provides voltage to the ignition coils during starting. This voltage is typically reduced to 10 or 101/2 volts while the battery is providing the current to crank the engine.

Often older bikes get hard to start for a reason explained in the following. Fortunately it's an easy and cheap fix.

Between the battery and the primary (low voltage) side of the ignition coil you have at least an ignition switch, and kill switch. Many bike have additional switches for neutral, sidestand or clutch lever.

When new these switches in series with the coil are no big deal. as they age, however, these switches can produce a small voltage drop that translates into a significant loss of voltage going to the spark plugs. Even a loss of 1/2 a volt will result in the loss of several thousand volts at the spark plug. (in low voltage industrial controls relay and switch contacts are gold plated to prevent this problem)

An indicator that this problem exists for you is if your bikes starts more easily if you've had the battery on a charger until just before starting. This problem also often causes hard starting on a warmed up engine. On my GL1500 the indicator was that the bike would crank and then fire just as I stopped cranking. The voltage rise which occurred due to the removal of the cranking load caused the engine to fire immediately.

The remedy for this is the addition of a 12v. relay. A wire goes from the battery (+) terminal (fused, if you are smart) thru the relay contact and on to the primary side of the coils. The original wire to the coil low voltage terminal is used to energize the relay. This approach maintains all of the functionality of the interlocks on the bike.

A $5 horn relay from NAPA works fine but any 12v relay will do since it is switching only a very small amount of current.

Many times owners of older bikes spend hundreds of dollars on aftermarket coils and wires when this simple fix will make the bike start like new.

Hope this will be helpful to someone. I used this to make my '88 GL1500 start better.
 

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cldryder is right on---go to KZRIDER forum and search under "coil mod" should find a wiring diagram that will explain modification.....worked on my 80 KZ750G like a charm, and it should work on GL's
 

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You'll just have to remember that you can now start the bike with the bike in gear and clutch lever not depressed. Could be dangerous if you're not prepared.

As far as the kill switch and side stand switch, as soon as you let off the starter switch when the bike starts, the engine will die, if either switch is on.

Just a thought.
I think you misread the original post. By using the original coil power wire to energize the relay you retain all of the interlock and protection devices.
 

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I approached it a little different on my 1100. I made everything but the ignition run off relays so if the relays fail it still runs and the load of the lights etc. is not on the ignition switch.
 

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Years ago I had a guy tell me his secret for getting 50s vintage cars going in coldest weather. He used one of those hot shot batteries like electric fences use. Wiired it up to the coil. Claimed it worked great.

gumbyred
 

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Low voltage to the coils at startup has long been a concern on the 1500's. I recommended a relay for startup some time ago and it fell on deaf ears. Seems a new battery solved the problem.
I still maintain a bypass relay is the answer to most 1500 starting issues. If you were to wire the relay in parallel with the starting circuit, the system would still be left intact and all safety features inabled.
 

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Low voltage to the coils at startup has long been a concern on the 1500's. I recommended a relay for startup some time ago and it fell on deaf ears. Seems a new battery solved the problem.
I still maintain a bypass relay is the answer to most 1500 starting issues. If you were to wire the relay in parallel with the starting circuit, the system would still be left intact and all safety features inabled.

you wouldn't have a wiring diagram to show to put the relay in would you?? inquiring minds
 

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Discussion Starter · #10 ·
wiring diagram

I do have a wiring diagram but its on my computer at work. I'll try to remember to post it next week. in the meantime you might be able to find it on the KZ1300 forum. thats the 1st place I posted it a few years back when I solved a notoriously common hard starting problem on a KZ1300.
 

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I had not read these "relay" tips. Excellent Stuff. Thanks
 
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