'73 Z9 burning out coils

[Benz]

As the heading says, the old [yellow...]zed keeps burning the left coil only, this is the third coil it has burnt through, and the last coil burntout/melted at the mains terminal after I installed a Dyna S system, which removed the faulty condensers fom the bike, and gave a fat regular spark that improved the engine's response markedly. I rode it for twenty klicks, all good, then the owner jumped onboard , and didn't get 10k out of it, before it went back to two cylinders again.[V]
I will check the earth terminals for corrosion when the bike returns, but...........any suggestions??? it's got me a bit fubared here....

[Dynomutt]

Make sure you are using 3.0 ohm coils with the Dyna S ignitions. I'd use the green Dyna 3.0 ohm coils. What tacho are you using? and where are you taking the feed from? I had similar problems using a Yamaha digital dash from an XJR400SP which would take out one side of the ignition, it killed whichever side I took the tacho feed from because the resistances were wrong, the Yamaha systems tend to use 2.2 ohm coils, the Dyna S is a 3.0 ohm system.

[Chris41]

Just make sure when trouble shooting with a Dyna S to check the sender modules they can start OK then fail with heat.
You can move them back and forward creating a spark while aiming a heat gun on them to see if they fail.

[Benz]

The coils are shorting the primary coil to earth,[melted plastic oozing out at the core mount point] in every case. The last one metered 2.7ohms across the primary terminls before the short , and then O ohms from the primary positive to earth/core ,and 500 odd ohms between the primary terminals afterwards, no doubt the coil failed. I am beginning to believe it is simply old coils, replacing old coils, and just not handling the job anymore. I have ordered two new 3ohm green dyna coils to replace the original, and its [3rd]blown buddy. If it blows these coils, I give up!
Dynomutt, this is an original Zed, so the tacho drive is coming from the head, by cable drive. The dyna S system has done 30k's, it had better not be failing...!
Thanks for the replies, I'll let you know how it goes....

[Redmohawk]

Check your output voltage from the Alt, if its over 15 volts I'd bet theres your problem. One coil may have a longer route/more resistance hence coil lives on one side.

Dyna S ignitions do not play up. They work or they don't. There's no in-between.

Make sure you do not have any voltage between earth and either terminal on either coil when the ignition is off.

While measuring for voltage, turn the motor over and see if you get any voltage spikes as the rotor passes either pickup.


Have seen similar results when ignition was left on on a dragbike with a Dyna-S and Dyna coils.

[Benz]

You may have given me the goods RMHawk! The bike was 'fixed' at a local 'professional' workshop initially, I discovered afterwards the main power terminal to the battery was near severed,[how do you miss this??] and the bike would run [poorly], but no starter motor, or lights, etc. So the alternator circuit had to supply the power vitually on its own, and some components in the rectifier/regulator may well have been fried.
Good tip, should have thought of this myself.... I'll let you know when I get the [dyna]coils in.