using a car coil for a bike

coil for one side of my bike failed . i have several coils from a 93 olds. on my meter they show 1.5 ohm but the spectre ignition im using calls for 3 ohm . can i use a resistor to make it 3 ohm or can i run it straight ?

That GM coil should be closer to .5 ohms.
To be safe, you will need a 2-ohm, 100 watt resistor. It will be big. Or use two 1-ohm, 50 watt resistors in series.

The resistors should be in series with the coil, of course.

I would estimate the coil should be charged to about 5 amps in about 2 to 3 milliseconds, so with the resistor(s), it should be a decent match for the ignition. However, if it is reading 1.5 ohms, the GM coil may be on it's way out.

Putting the resistor in series reduces the voltage at the coil, so it will have less spark energy. Z1 sells an OEM type EMGO coil for about $36. Do it the easy way, get the right coil.

i must be looking at a different z1enterprises than you only one i see is 87 for one or 130 for a pair to fit a spectre

For consideration --

www.z1enterprises.com/detail.aspx?ID=2857

www.z1enterprises.com/detail.aspx?ID=4333

www.z1enterprises.com/detail.aspx?ID=4334

Good Fortune!

I'm currently running the top one listed in the above post.

those are 4 ohm is that compatible with the electronic stock spectre ignition?

btchalice wrote: those are 4 ohm is that compatible with the electronic stock spectre ignition?

Not really. They would charge too slowly for the dwell given by the ignition.

The GM coil is a better match for charging times. That GM coil is meant to be used on an ignition with a current limiter. That is what you would be doing with the resistors, as you had planned.

What Bountyhunter says about the spark energy being reduced due to the voltage being reduced is true, but it would not be much different when used on a car. You would be limiting it to about 5 amps, and that is in the range of what the car would do as well. They might limit it as high as 6 or 7 amps, but since your dwell will be longer at idle, you run the risk of heating the coil more than it would like. You could adjust your resistor value downward accordingly if you need a little more spark energy. But I would try it first before pumping more amps into the coil.

Any lower-inductance coil tends to store less energy than most high-resistance, high-inductance coils, so it is true that getting the right coil (probably 2.3-ohm is correct) is best for spark energy. But if the engine is in good tune, you probably won't need the extra spark energy and may not even notice it. So if money is an issue, and you already have the coils and wires and have a way to mount such huge coils, then I'd try it. As a matter of fact, I actually had one of those coils and worked out an ignition circuit to use it, but the damn thing was too big to fit under the tank. Too bad, they are really cheap and plentiful.

btchalice wrote: those are 4 ohm is that compatible with the electronic stock spectre ignition?

IMHO, you would be hard pressed to detect the difference running a modern 4 Ohm coil in place of an old design 3 Ohm coil. If any difference, only at very high RPM near redline. The higher impedance means the charging current is about 30% less (compared to a 3 Ohm coil), which may slightly reduce stored energy in the coil. But newer coils are more efficient anyway. It would probably run fine.

was wondering, can I re-locate my coils on my 82 kz 1100 spectre d1? they are located right abouve the motor and I'm concerned about the heat. I would like to move them to a more ventilated spot. but will it causeme a problem with spark delivery ??

coils have been on and around engines since almost the beginning the heat there unless you sit idling for long times isn't so bad

cool, thanx. was just making sure I wasnt looking at a future problem