Help on my KZ750 cylinders 1-4 aren’t firing.

So on my way home tonight I was driving everything seemed fine. No problems. After about 30 minutes of on the interstate my bike all of sudden my bikes cylinder 1-4 cut out and stopped running. I was able to get her started and on two cylinders and get home. But I don’t know why one coil would have no power and the other would. Is my coil bad? Could a lose connection cause one coil to stop working? Any help would be appreciated. I’ve had some charging issues in the past idk if they’re related or not. And I feel like I remember this happening before but last time power was cut to the entire bike from what I remember. Same thing happened but it happened like a year ago and I haven’t had any problems since. I’ll fiddle wi the the wires another day and see what I can find.

Thanks!

Check and clean all your connections. If that doesn't solve your problem then try switching the coils around. (You will need to rewire them accordingly.) If 1 and 4 work with the coil from 2 & 3 then the problem is likely the coil. You can check it by measuring resistance on the primary (sparkplug wire to sparkplug wire) and secondary sides. You should get 2 to 4 ohms on the primary and 15k ohms on the secondary, or perhaps higher. If the resistance checks out then the coil is OK and your problem is either in the pickup or in the exciter, if you have one. (I'm assuming you don't have points.)

Okay. Will do. I’ll try to that sometime this week if I can. It’s got a dyna s ignition system I installed way back when I built it.

Do the pickups wire directly to the coils or do they wire to an exciter and then the exciter goes to the coils?

Straight to the pickups. It’s a very simple system. Power goes to the coils and then you have the wires from the pickups. That’s it.

The first thing I'd do is redo all of the spark plug wire connections. The plug wires unscrew from the coils by unscrewing the ribbed compression boots. Untwist the spark plug caps from the plug wires. Nip off the ends of the wires a tad to freshen up the connections, especially if they have the greyish oxidation. I solved an intermittent firing problem by doing this (but later on replaced the coils w the green Dynas & installed a Dyna spark plug wire set).

Next, if that doesn't solve the problem, I'd swap the ignition coils to see if the problem follows the coils

You could also use a meter to test stuff. An ignition coil can test fine cold but fail under load when the engine is running.
I think some guys heat them with a heat gun to mimic running conditions.

I agree with all the above. I’d start with the least destructive test first. Pull all the plugs put the back into the plug wires and lay them on the engine case. Make sure they have good contact. Crank the bike over and look for spark. This is better done in a dark garage or at night. You need a meter and test voltage at the coil primary. Just remember when testing individual coils the both secondary’s need to be grounded for an accurate test. The last page has some trouble shooting.

So no exciter. That means the coils should be 3.8 to 4.2 ohms on the primary side.

If two cylinders won't fire, it means the likely cause is either the coil or the pickup or the wiring.

1) Check the wiring for any unplugged wires. Clean all the contacts. Still no spark?

2) Check the coil for correct primary and secondary resistance. A short in the coil means it must be replaced. Coil is OK?

3) Your pickup is probably shot. Replace it.

First thing I'd do is check the battery to make sure it's properly charged.

What I'm about to describe isn't the source of your problem but I've had trouble with this in the past. Look at P2 of the information Mikaw posted. At the bottom you will see how the power for the pickup is transferred through a hot connection on the bike via a push clip. That push clip often makes a bad connection, which interrupts power to the pickup. I have Dyna on all my bikes and I attach that red wire from the pickup directly to a hot connection on the bike. On the 900's/1000's there is a spare brown wire near the headstock that will provide necessary power. I'm guessing (but I don't know) there is a spare hot wire on your bike as well.

The same thing happened to me. One of the wires going to the coil for 1&4 had just come off. Hopefully your solution is as simple...

I have experienced on more than a couple occasions coils that work when cold, and then fail when hot.

Mike