Coil mod

[Nightengale]

I was just wondering if anyone has checked the voltage at the coils to see if you have the full 12 volts at the coils? I haven't checked mine, but am getting ready to. The reason I ask is because I just built a 76 kz900 and with the old wiring I was only getting like 10 volts at the coils. And I did a coil mod where I ran a wire from the battery to a car relay that was connected to the ignition, a ground, and connected to power the coils. So as soon as you turn on the ignition it has full power to the coils. It eliminates the power from having to go thru the whole harness before getting to the coils. Pretty simple mod and works great. Do you guys think this mod would be benificial to our bikes? I do have a diagram but can't find it now. And it is pretty simple and cheap to do.

[natemoen]

There are a few people here that have done that.

[bikerphil]

I've run both my XS11's with the coil relay mod, I also power the stock horn thru the same relay. Been running this way for years with no problems, just the positive results of a hotter spark and a horn that 'blows'. We call this voodoo electronics.

[TomB]

Yes I think its beneficial, though running the coil wiring unprotected, no fuse, is a concern to me.

I wired our drag bike the same way, a lot of drag racers run without fuses as they don't want any weak links, which is exactly what a fuse is.

[Nightengale]

Fuse

Sorry forgot to mention there is an inline fuse between the battery and the relay.

[trbig]

a lot of drag racers run without fuses as they don't want any weak links, which is exactly what a fuse is.

My bike's weakest link sits on the seat.

[Nightengale]

Straight wire

I know some guys that have done it without the relay, and used a toggle switch instead. The kz I did had about 10 volts before the mod. Now has the full 12. A lot easier to start and runs better.

[James England]

Yes, it's supposed to be a good mod, by all accounts, and gives better voltage at the coils, especially on older bikes with older wiring, a a circuitous route via the wiring loom to the coils....

[Nightengale]

Pic

[DAVINCI]

instead of adding another point of failure, I would correct the wiring deficiencies

JMHO

[D0wn5h1ft]

Is there a tech tip with a guide on how to do this "coil mod"? I'd be really interested in trying it out.

[mikubuilder]

that diagram above should be self explanatory :P

[TomB]

My bike's weakest link sits on the seat.

The drag bikes owner/rider is often called "the nut that holds the handlebars!"


And me and the other crew/mechanic often called his "carers", it does take a certain kind of lunatic to launch one of them things. But I digress.

So is it possible to correct the OE wiring failures? or does the OE wiring have enough wiring, connectors, other feeds from the red/white wiring to give enough resistance to reduce voltage to 10V? I know the red/white wiring goes through the right handlebar kill switch which is a point of voltage drop if corroded, the relay mod does keep the kill switch but does take the losses out of the circuit.

[D0wn5h1ft]

What are the electrical specifications of the relay? 12v but what should the rated max current be? I'm not sure what kind of current the primary coils need at steady-state.

And I assume, without looking at a circuit diagram, that the actual switching of the primary coils happens on the ground side?

[crazy steve]

You want a relay with a minimum rating of 15 amps; higher would be better. There's a inrush current factor that can give current spikes of up to 300% of the 'rated' current.

Although I agree with Davinci; if you have a serious voltage drop to the coils, you have issues in the harness and this simply bypasses it, it doesn't fix the problem that is probably indicating other issues that you may not be aware of.