How commom are cracked coil cases?

Both of the coils on my KZ750 are cracked, along the circumference, about 1/2" to 3/4" from the front end where the ignition leads from the CDI attach. They're not cracked all the way around, but each one has a crack about a inch and a half long.

I just ask because I'm trying to diagnose an issue that appeared suddenly as I was going down the road awhile back. The bike stutters between pulling cleanly and stalling. I've several things to check yet, including just how good the carb boot to head seal is, so this coil issue is not necessarily my main culprit. It doesn't appear the coils got cracked overnight.

The cracks usually come from heat.

Leaving the ignition on for more than a few seconds can overheat a coils.

If your regulator has failed, you willl be pushing 17+ volts through your ignition system. This will often cause coils to overheat.

If you look for new coils, just beware, the factory coils are not actually CDI coils even though some retailers will label KZ ignitions as CDI. They should be 2.5 ohm coils, and 3 ohm coils should also work.

A good place to get coils is here .

As Jeff said Heat is the problem. some bikes more than others. The KZ1300 is notorious for this I doubt there is one out there that still has original coils. Both of mine had all three coils cracked by 30,000 mi. I am not sure of the 750, but it is a period bike. i would get a set of aftermarket coils but as mentioned before, make sure they have the right resistance for your ignition.

Get yourself some new coils from Z1E and make sure you've got full battery voltage at the primary terminals BEFORE you install the new coils.

EDIT: Ooooops!!!:blush: My error as loudhvx nicely reminded me. What was I thinking ??? Good thing I never tried to become an electrician.:blush: Evidently I need to brush up on Ohm's law.....quite a bit. I'll just go to my corner now and contemplate the mysteries of voltage drops and fixed resistances.

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Good info all.

And yes, Z1 is where I would go for coils.

Would cracked coils cause a situation where the bike was running fine, and then all of a sudden started to hesitate like there was water in the gas or some-such?

yes it could and as few other people have said it can be quite a comman problem. if the coil has a big enough crack to allow moisture in it cause it to break up as well if the crack exposes the windings to a ground source [the frame ] at higher outputs it can bridge the gap from coil to the frame instaed of at the spark plug electricity will always take the path of least resistance. it is really comman problem on kz1300 but i have found cracked coils on just about every type of bike over the years so it is not an isolated problem.

the coils on my z1r cracked and i rode it for a couple years.it seemed to run fine,no plug fouling,but you could not wash it or it would not start for awhile(till the coils dried out).then i put jb weld on the cracks and rode it several months more(still couldn't wash it tho,only by hand where the water wasn't gettin to the coils).then one day last fall i was the last bike leaving the bar and flogged it to catch up and smoked both coils at the same time.
got new dyna's now and i wouldn't mess around with filling the cracks again,just buy some new ones.now the bike starts much easier,i'm sure it wasn't good for me to run those coils as long as i did.

leon holmes

if the coil bodys are cracked bad enough the windins in the secondary can actually seperate not something i would really want happening underneath 3 gallons of fuel.

timebomb33 wrote:

if the coil bodys are cracked bad enough the windins in the secondary can actually seperate not something i would really want happening underneath 3 gallons of fuel.

I'm not going to argue with that!

Do the Dyna coils mount right up to the factory locations or do you have to fab something up?