As a recap: 1985 K100rs (2V) Generally ran well..... Some dificulty starting.....drops a cylinder or 2 every now & again at slow idle, seems ok above 1200 rpm. Also causes it to buck & stall if cylinder drop out happens to occur while engaging the clutch.

Troubleshooting section found elsewhere in these forums (excellant) shows an Ignition coil seconday resistance of approx

12.6K Ohms. The coil in the photo appears to be somewhat different than the ones I have.

Tested Mine 1-4 = 17.2K, 2-3 = 10.2K

Tested spares on a "parts" bike. 1-4 = 17.2K, 2-3 = infinity/open (assumed defective)

Installed the 1-4 coil off the parts bike to replace the low impedence 2-3 on the runner.

Now starts & runs normally. Also picked up about 300 rpm at hot idle.

Conclusion, proper secondary resistance value for this model is closer to 17K ohms that the 12.6 shown in the trouble shooter. Primary resistance checked about 3.4 on all 4 of mine.

Can you say if the coils that have the orange high tension towers turned out to be an improvement over the early ones with all black?......Or was it just a change in suppliers?

I turns out I was wrong. Replacing the coil with a used one has not solved the issue.

I just got a set of orange tower coils. I am dismayed to see that I would have to get different spark plug leads (or ends?) to use thse coils due to the stud in the center of each tower. Second, would require some upgraded primary wire connectors to power them up.

Last Unknown. The primary resistance on the original coils is near 2.6 Ohm. The newer (16 valve) orange tower ones are only 1.5 Ohm. I believe they are designed this way, not defective as they both match and look very "new".

Will the 1.5 primaries work CORRECTLY with the ICU designed for the 2.5 Ohm coils?

I would like to hear more detail about the upgrade to Orange towers the owner mentioned earlier here talked of.

Run the engine in the dark and look for sparks...certainly how Rossco and I found his dodgy electrics.....of course the ticking sound (in time with engine miss) was a dead give away too.....good luck mate.

As an aside when we insulated the cracked coil the idle improved heaps and was also great to start every time.....and made the carby tuning possible!!!

ibj ...it was common practice to go to lower impedance coil to try to beef up the spark output around the 90s

we have to remember that the silicon used for switching these lower impedance coils was made for the job .
in fact many of these newer series have what is termed ignighter modules (really just offboard switches to power those coils )


our older computers may well fail if asked to drive almost twice the current to the coils from the later series .

good luck with your quest ....but my suggestion is stay with higher impedance coils and get them and the ignition leads etc right !

Thanks, I'll try to re-sell the 16V coils I bought & search for another solution. Here's another tip I've known but never seen posted here:

If you put a few drops of dishwashing detergent in a spray bottle & fill it with water......then just "dust" the Ignition wires with a slight spray......those pesky little spark leaks may start to show up even better.

I' going to check my running battery voltage before anything further to be sure I have enough to run the coils efficiently.

ibjman wrote:I just got a set of orange tower coils. I am dismayed to see that I would have to get different spark plug leads (or ends?) to use thse coils due to the stud in the center of each tower. Second, would require some upgraded primary wire connectors to power them up.

Last Unknown. The primary resistance on the original coils is near 2.6 Ohm. The newer (16 valve) orange tower ones are only 1.5 Ohm. I believe they are designed this way, not defective as they both match and look very "new".

I would like to hear more detail about the upgrade to Orange towers the owner mentioned earlier here talked of.

The improved version coils with orange HT towers for the 2V have different connectors
than the 4V coils, both primary and secondary side.

2V coils:


4V coils:

So, I just bought the wrong orange tower coils. Do you think I'd have any luck finding someone with some nice 2V orange tower coils that would like to trade me for my very nice 4V orange tower ones??????

I've seen several posts here asking about an miss or stumble low speeds & at idle. Originally, I found mine to be much improved if not cured when I took a used coil off another machine. In the long run, though the pesky elusive stumble/miss (worse at 100RPM or below kept popping up. Most annoying if you "dog it" when releasing the clutch from a stop light......if the stumble happens to ocurr at that moment it bucks & stalls (bad news if the car behind is not paying attention. The coils seemed all right and you could not identify what cylinders were missing by pulling off a spark plug wire. The miss only seemed to be partially not firing on 1 sometimes 2 cylenders. Tested in the dark looking for tel tale "blue sparks" leaking off the coils or wires, again no problem found. Even sprayed a light mist of watter all over the ignition while running to try to create a failure. Nothing seemed to help.

Finally, I bought some vacuum gauges & built a sync set. The miss at idle seemed to almost disappear after carful adjusting but still on road, if you tried to "load" the engine at very low rpm, the miss & stumble still happened.

Today, I recieved a used set of the updated "orange tower" coils (the ones for the early 2V model.

I'm happy to report that the machine runs like a "New" one now.

Thanks to all the members here who spent countless hours trying to help with this! You guys are the best!

yay a great result ibj ....cheers !