7 ohm blue Dyna coils on a KZ650 B2 ?

I need to change the ignition on my 1978 KZ650 as the original coils melted...
Ultimately the plan is to also switch the ignition for a Dyna-S module.

Can I use the blue Dyna 7ohm coils? What's the main difference with the 3 ohm green coils everyone seems to use? I've been told that the blue coils will be easier on the bike's electrical system... Can anyone chime in on this?

Thanks!

BTW, the bike is a daily driver, not a track/race bike.

If you're going to add a Dyna S use the green coils, they are matched to the Dyna S ignition and will offer the best performance/reliability. Plus the 3 ohm coils will work well enough with your stock system until you switch to the Dyna S.

3 -ohm is the minimum Dyna recommends for the Dyna S. That will produce the hottest spark at higher RPMs. Any lower, and you run the risk of burning out the Dyna S.

The Dyna S nearly doubles the dwell angle, and thus the dwell time at any given RPM, compared to the stock points. Because of this, the coils get double their typical average current. This means the bike's charging system has to provide nearly double the average current to the ignition coils. This indeed does tax the charging system considerably. All of this is if you are using the stock 4-ohm coils. If you go to the 3-ohm coils, it taxes the charging system even more.

The benefits of the extra dwell are only realized at higher RPMs. At lower RPMs, the extra dwell is only wasting power in the form of heating the coils unnecessarily.

If the bike ran good, originally, with 4-ohm coils and points (which only had 180 degree dwell), then it should run good, if not better, with 4-ohm coils and the Dyna S (which approaches 360 degree dwell). That is assuming the coils are like new, and can handle the extra dwell (and heat) caused by the Dyna S.

7-ohm coils will reduce the average current useage, but at the risk of less spark energy. It may greatly reduce the benefits of the Dyna S at higher RPMs. I wouldn't recommend the 7-ohm coils. They probably won't work with points or other electronic ignitions like the factory Kaw ignitions.

If your charging system is rock solid, and you don't spend a lot of time idling in traffic, then get the 3-ohm coils. Otherwise, 4-ohm coils will save you some electrical power, and will work fine with points.

If there is a chance you would consider the factory electronic ignition (which is far more efficient on power), then you'd want 3-ohm coils.

The Blue coils are NOT seven ohms - they are ZERO POINT SEVEN (0.7) ohm - and not suitable for the Dyna-S.

They are very high energy race coils =- to be used with an ignition like the Dyna 4000.

If you are staying with the standard points ignition, the best choice is to use an OEM 4 Ohm coil. Z1 sells them at a very reasonable price, or did last time I looked.

They might also work very well with a Dyna ignition designed to work with a 3 Ohm coil, as it will not affect performance much to increase the impedance slightly. As mentioned above, using a coil too LOW in impedance can blow the ignition.

colorfull wrote:

I need to change the ignition on my 1978 KZ650 as the original coils melted...

You will need to check your regulator. I suspect it has failed. When you get the bike running, check the voltage across the battery terminals. You don't want to be seeing anything higher than 15 volts at 4,000rpm or more. Ideally it should be around 14 volts.

Thank you all for the help.
I'll probably save a bit and get the complete kit from Z1.
But before I'll take your advice Jeff, and check the electrical system first.
The KZ won't be out anytime soon, bummer, because in downtown traffic I like it better than my Ducati. But at least I won't be walking!

Cheers!