Coil problem, need help

Hi,

I had a problem with poor sparks etc and made the recommended coil mod, everything went ok but now the bike only fires cylinder 2,3 occasionally (hate these non-consistent errors). I thought it was a bad connector at the 2,3 coil, cleaned it and the bike went as a rocket....for five minutes. I have cleaned all connectors I can find, have good voltage at the coils, good battery, new plugs, cleaned the spark plug connectors. So I need help, I have searched around and found that sometimes a coil can die when warm. Is there any sure way of testing that? I am rather new to bike electrics and if anyone have an idea I would be very grateful.

I will try to answer your question like this... it MAY be a bad coil but it is also possible that the coil IS NOT the problem. When a coil dies, it is by heat, like most electronic stuff on a bike. The coil is up out of the airflow and gets pretty warm when the key is switched on. A coil is made of two sets of windings which are copper wound wire coated in insulation (plastic stuff I guess). When they get hot, the insulation will eventually fail. If the failure is in two places and the places touch, you get a short. When a coil shorts, it won't work as it should...

OK, to check the windings for shorts, you need to test the resistance of the primary windings and the secondary windings.

Get a multimeter and set it in Ohms scale. The primary winding resistance check can be made by taking the two probes and touching them to the two lugs on the front of the coil where the power and ignition wire are connected. DO NOT touch the probes to the bike's frame or any ground. Leave the ignition switched off. Keep the meter in Ohms scale on a low value. The primary windings for MOST KZ bikes will be ~2.5 to 4.5 Ohms. If the primary windings are shorting, you won't get anything (infinity). The secondary windings are a tad more trouble to check. You should really remove the plug wires but most Kaw coils have the wires molded in so just pull the spark plug caps off the spark plugs and touch the meter probes to the conductors in the plug caps... in other words, on the 1 & 4 coil to the metal doohicky inside the plug cap of #1 and #4 spark plug cap. Put the meter on 20K Ohms scale. The reading should be between 11K Ohms and 18K Ohms or so... This figure will vary quite a bit as when the coil gets old, the resistance will want to creep up. It is sometimes very difficult to get any reading when checking the secondary resistance.

Anyway, since your problem seems to be sporadic, keep in mind that if there is a short, it too will be sporadic and the coils MAY test just fine but still short from time to time. Examine the coils for any cracks because they will short if there are cracks. I fill the cracks with JB Weld if I feel too cheap to replace the coils right then. I have a set of Dyna coils that I repaired about 4-5 years ago that were badly cracked and shorted when it rained. I repaired them with JB Weld and they continue to work just fine.

Last, a better bike shop may have a coil tester. These gizmos are a tad expensive for the shade tree mechanic but if you call around and find a shop with a coil tester, they may let you bring the coils in and test them. If you need to replace, Dyna coils are pretty inexpensive compared to what they used to be and www.z1enterprises.com has some of the best prices.

Thanks a lot for the quick responce, the resistancies are 2,4 Ohms and 24 kOhms. The coil looks ok but it is the original one. Is there an easy way of checking that the green cord connection to the coil is ok?

Would first assure having consistent power to the coil.

On KZ900, there's an under-tank wire with a dual connector. One wire from the connector feeds positive to 2/3 coil. Second wire feeds 1/4 coil.

Suggest checking for an internal break inside wire from dual connector to the 2/3 coil.

Such internal breaks do happen, and may exist regardless of wire's external appearance. Mine was discovered by manipulating the wire while using an ohmmeter to watch the on-again-off-again conductance. But believe could be tested by jiggling the wire while checking for spark in the usual manner (plugs removed and grounded against head while spinning engine over in neutral with ignition turned on).

To properly function, the coil requires a good continuous uninterrupted electrical supply.

Hoping for you a simple and inexpensive remedy.

Thanks, I have actually changed the power feed to the coils so that on I am pretty sure is ok. I am unsure of the other cable though. I will swap the 1,4 and 2,3 coils today and test and see if anything changes. If the problems move to cyl 1,4 I guess the coil is the problem.

The "green cable" is a green wire and it is the wire from your igniter box going to your coil that carries the ignition signal. To test this wire, use a multimeter on Ohms scale and check for end to end continuity by putting your probes on the end of the cable by disconnecting the Igniter connector and putting one probe on the pin that corresponds to the green wire and the other end of the green wire. If you have continuity, you will see a 1 on the meter. If the wire is broken, you will get changing values.

Thanks, will test this evening, wire of course I meant, beeing a Swede sometimes the language gets directly translated. Wire in Swedish could be said as "kabel":blush:

So this evening I tested the continuity of the green wire, not 0 ohms but 0.2 but I guess thats ok. And now the bike works again. Took a quick ride and all ok. Will test a longer tour tomorrow. Man I hate non repeatable errors.

Gotcha! your English is probably better than mine! For a Texan, we say "WHARR" not wire anyway hehe