TOPIC:

Hi,
as my coils are ~40 yo and the plastic is so old that it cracks I'm looking for replacement coils.
Could you please review my findings and tell me if they are correct before I buy some expensive new coils ?
What I found is:
- the original coils should have a primary winding resistance between 1.47 <-> 1.63 ohm.
- there is furthermore a ballast resistor of 1.5 <-> 1.9 ohm.

That's a total of more or less 3 ohm.

So I can either:
- remove the ballast and buy a pair of 3ohm coils
- don't touch the ballast and buy a pair of 1.5 ohms.

Right ?

Furthermore, what's the point of having this ballast resistor ? On old 6V cars I know the ballast was bypassed when the motor was cold in order to get stronger sparks but as far as I know there is no such thing on a ST ?

Did you try to use coils with a lower resistance in order to get stronger sparks ? I know the coils could end up burning (I've already seen this on a VW bus...) but maybe there is a safe margin below 3ohm ?

Finally, as the ST already has an electronic ignition (hall effect sensor) there is no point in mounting an aftermarket electronic ignition system right ? So is there any other mod to get a stronger spark ? I've already heard of WiredGeorge mod and plan to do it btw.

Thanks.

The factory electronic ignition for Kz's are designed to use 2.3 ohm coils. They measure from 1.8 to 2.8 ohms, usually toward the higher end. But I suspect the earliest version came out before the 2.3 ohm coils were available. Since the dwell on the ignition requires a "faster" coil, that is a coil with lower resistance (and inductance), they had to use some low resistance coils, which could potentially harm the igniter unit due to over-current. In order to prevent that, they added a ballast. The later models, which had 2.3 ohm coils, did away with the ballast.

The ballast is not really ideal, as it basically just wastes power, as heat, in order to lower the current in the coils.

You should remove the ballast and try to use coils that are in the 2.3 to 3 ohm range if you have the factory ignition.

The points-driven Kz's use 4 ohm coils, which are a bit too slow for the electronic ignition. They may work at lower RPMs but not at higher RPMs.

The factory ignition did not use hall-sensors. The pickups are variable-reluctance pickups. If you have hall-sensors, then you have an aftermarket ignition, most likely a Dyna S. In that case you need coils that are 3 ohms or higher. The Dyna S works fine with 4 ohm coils as well.

Dyna makes very good 2.2 ohm coils that are very well matched to the factory electronic ignition. They also make a very good 3 ohm coil for use with the Dyna S. Accel super coils come in 3 ohms too, and they seem to work well.

Because the dwell is not precisely controlled on the factory ignition or the Dyna S, you must use a full-size coil, and not a "mini" coil. The larger, "full-size" coil can deal with the extra heat dissipation required when the dwell is longer, like at idle. Small mini coils tend to overheat in that situation.

I've been using no-name, 2.3 ohm coils from ebay (they look exactly like the 2.3 ohm factory coils). They can sometimes be found at less than half the price of Dyna coils or Accel coils.

You're right, I checked the specs and it's indeed not a hall effect sensor.
I'll follow your advice and buy a pair of no-name full size 2.2/2.3 ohms coils.

Does anyone have another trick to get stronger sparks ?


Edit: are the dynatek dc4-1 coils the right "reference" coils ? www.z1enterprises.com/dyna-dual-output-2...m-coils-1-dc4-1.html

The factory ignition, when working properly, has plenty of spark. The most common cause for weaker spark is voltage loss to the coils due to bad/dirty connections. Most commonly the greatest loss is at the fuse holders and switches.

The relay mod bypasses the bad connections, but is just a band aid masking the underlying problem. This may get you running better, but more problems may arise down the road unless the real problem is corrected. Patton has some good graphics on how to check for voltage issues.

The second most common cause for weak spark is probably old coils. That grey dyna dc4-1 is the correct coil for the factory ignition. However if you are considering the possibility of going to a dyna s ignition, due to a possible problem with the factory ignition, you may want the green dyna coils that are 3ohms. They look like the grey ones, but are green. They are not perfectly matched to the factory ignition but seem to work well with it.

The dyna s requires 3 ohms or higher.

And of course, you need two, and I think the kits with two have a slightly different part number.

You may want to do some troubleshooting first to rule out the possibility of a bad igniter and/or bad pickups. If you have at least one good coil, you can troubleshoot by simply swapping some wires around since you essential have two ignition systems, one for each pair of cylinders.

I've checked the voltage, when I have 12.8V on the battery I have 12.4V on the coils, so its not perfect but not disastrous either, I think there will be no huge improvement if I rework the wiring assembly or do the WG mod.
On the other hand my coils are in a really bad shape so I have to change them anyway, so I'll first do that, see if there's an improvement and if I still have weak sparks I'll dig further.
Thanks for your answers.

Hi
I got my Dyna 2.2ohms coils, the old ones were actually badly damaged (melted on the back side):

The Dyna coils seem to work well without the ballast resistor, I hadn't the opportunity to ride yet because of many other problems I have to fix but at least the motor starts and revs up.

Wow, those coils are toast. I wonder how they got that way. If someone ran it without the ballast, that may have done it, or if an igniter shorted out previously.

The new setup looks great. Nice job.

Thanks!


Toast is the right word indeed, I have no idea on what happened and I'm even surprised I was able to ride with these.