TOPIC:

So I want to test my coils using a voltmeter, but I don't exactly know how to do it. What do I set the meter to? Do I check the primary AND secondary sides?

I assume you really mean a multimeter, not purely a voltmeter, right? You're talking about checking the resistance, not the voltage, right?

You will need to use the Ohmmeter function of your multimeter. You will need to check both the primary and secondary resistance.

Do you have a service manual for your bike? The procedure should be described in there along with the tolerance limits.

For my 78 KZ1000, the accepible tolerances are:

Primary winding 3.2 to 4.8 Ohms
Secondary winding 10.4-15.6K Ohms.

yes I mean a multimeter, sorry...
and I don't have a manual. I'm really just testing to see if my coils are bad. I've been having ignition problems and after all the troubleshooting I've narrowed it down to a bad coil or....well....I don't know...haha

Good luck with your coil tests. Heaven knows I'm not any help there.
But Im dying to see a larger pic of the Z in your avatar. I love those Dunstall-type pipes. Is the bike yours? Details man, details!

Not so oddly, most of the manuals for these bikes are written for an analogue meter, rather than digital.

This makes significant difference when testing coils and diodes due to the greater output strength in an analogue meter as opposed to digital. Not to mention that troubleshooting requires a different technique than what is laid out in the manuals (can't test a diode using the Ohm's scale on a digital meter).

Next time your at a flea market and spot an old Simpson, grab it.

The meter should only make a difference on non-linear semiconductor items (like diodes, ignitors, and regulators). To a coil, measuring the resistance shouldn't make a difference whether you're using a digital or analog meter.

I (mildly) protest Loudhvx;.

After reading many of your posts, I would not be surprised if none of this is news to you. Perhaps to the benefit of those who might read it, I`ll take this opprotunity to go on a tangent.

Ideally, Bicycle Lee would test the coils for voltage as this is the most direct route to observing a value with out having to worry so much about losses due to poor connections. Realistically, a significant difference in AC voltage output between windings (meaning phases, not primary and secondary coils) is a more clear sign of failure than resistance.

Coils are not purely resistive, they are inductive - inrush currents in a coil are substantially higher than operating current, making it difficult to get a true reading in the less than ideal environment of a motorcycle harness.

When measuring resistance using a multimeter, Voltage is induced into the circuit by your multimeter (both analogue and digital) in the resistance setting, the amount of current flowing between the leads is measure and the resistance of the circuit is hence calculated. The output voltage is much higher in an analogue meter than DMM (typical 12VDC vs. 1.2 to 6VDC)

If resistance is the test of choice, an analogue meter having greater circuit voltage may help to find a 'weak' or 'break down' winding where it may be hidden to a DMM.

Overall, the analogue meter is a much better tool for our needs than a DMM due to the jargon in the manuals we trust and the sketchy nature of some repairs exectuted by PO`s we`ve read about here, which is the point I was trying to make.

Saki, all protests are welcome. I certainly am not the last word on any of this.

Saki Jockey wrote:

If resistance is the test of choice, an analogue meter having greater circuit voltage may help to find a 'weak' or 'break down' winding where it may be hidden to a DMM. .

Yes, I see what you're saying now. I haven't noticed much difference in using analog versus digital, in this respect (measuring primary resistance on coils), but your theory is correct. The primary side typically withstands voltages in the 400 to 600v range for every spark, so I wouldn't expect to see a lot of difference between a 9v analog and 1v digital meter, but it's certainly not impossible.

Saki Jockey wrote:

Overall, the analogue meter is a much better tool for our needs than a DMM due to the jargon in the manuals

I agree on that. Even if the manuals are written for DMM's, DMM's vary widely from the $2 cheapos (yes I've seen them for $2 at Harbor Freight and own several), up to several hundred dollar Flukes.

I use a Fluke 189 for my daily grind, an old Simpson for nostalgia and an 'scope just to scare the absolute crap out of my clients when their complaining overcomes my patience.

My comments are incomplete re: analogue meter for coil.

increased voltage also stipulates increase current, load (coil) remains constant. Coils in an ignition system are really nothing more than transformers. DC will not continuously pass through a tx unless it is pulsed, perhaps it may show signs of failure if used as a load singularily and continuously...

I've gotta find some old coils and play with this.

BL... Not sure if you had your question answered... with a multimeter, you can check both the primary and secondary resistance as well as voltage going to the coils. There are two sets of windings in the coil; primary windings and secondary. By measuring the resistance, you can get a sense as to whether the windings are in good shape. The windings have insulation that once melted, allows the wires to touch and short. When the coil shorts, it doesn't work.

To test the primary windings, put the meter in Ohms scale on the lowest scale (X1 usually). Touch the two small lugs with wires connected (with power off). Most coils used with IC Igniter or points ignitions will have 3 Ohm primary resistance. If your coil has an infinite value, then its primary windings are shorted. If the coil has LESS than 3 Ohms, it may have the correct value as some Kaw models use a ballast resistor to get the cumulative resistance up to where it needs to be. Resistance can be up to about 4.5 Ohms and the coils is still OK... When they age, resistance can drift upwards and the coil will not fire as well as it should... I have seen 3 Ohm coils (designed to be 3 Ohm) read as high as 10 Ohms. If you find this situation, you should replace the coil as the spark will be lousy.

To test the secondary resistance, it will be higher so set the meter to Ohms but on a scale where you can read 12-20K Ohms. Various coils will have secondary resistance values in this range... not sure exactly what yours should be but if both coils read the same and are in this range, they are probably OK... again, you don't want to see an infinite value when you probe... to test the secondary values (bike isn't running), put the probes on the metal plug connects you see if you remove the spark plug wires. If your wires don't remove, put your leads on the spark plug cap metal conductors. It is sometimes hard to get a value using the latter check points. If you find infinite value, you have a short and the coil needs replaced. If you use the plug caps and find nothing, this isn't unusual... like I said, sometimes hard to find a good contact so move the probes around on the metal.

Last check with the meter is voltage. You can see the steps for this on our website under "Coil Repowering" if you follow the "wg's Tech Stuff Index" link. Our website is in my signature. This test is for testing DC voltage at the coils.

thanks WG....that's info I can use.
when you say plug connects you mean underneath the rubber cover on the end of the spark wire, right?

Post edited by: Bicycle Lee, at: 2007/10/14 11:48