KZ1000 misfires and runs rough when hot

OK my KZ1000 runs great for about 6 miles then starts to misfire and spit and sputter after she gets warm. It misfires at all rpms but almost dies at idle. Everything I've read says misfiring when hot is an ignition problem. I suspected a thermal short in one of the coils or a problem with the pickup coils. So I ran through the resistance checks of both suspects cold and hot with the following results.
Cold
left and right coil primary resistance = 2.4ohms
L and R secondary resistance = 11.24K ohms and 11.74K ohms.
Pickup coils yellow/red 424ohms and black/green 424ohms.

I let her idle in the driveway for 10 minutes before she started misfiring again. I kept her running another 10 minutes then retested the hot condition with the following results.
left and right coil primary resistance = 3ohms
L and R secondary resistance = 13.5K ohms and 14.2K ohms.
Pickup coils yellow/red 480ohms and black/green 481ohms.

This seems well within spec. I can pull each plug wire and keep her running at higher rpms but she'll die at idle pulling any one of the plug wires. Pulling #4 seems to have the least effect.
I don't suspect the igniter because it's located well away from the engine and isn't hot to the touch.

Any ideas would be appreciated. I'm about ready to take it to a shop but don't want to overlook something simple.

Possible sparkplug cap(s) failing when hot would be my guess. Look at this guide I made for the Kawasaki electronic igniton motorcycles:

Ohm Checking Pickup(Pulsing) Coils

The pickup coils on the Kawasaki’s with the factory supplied electronic ignition can sometimes fail or become intermittent due to heat and vibration.

1.Trace back from where the pick up coils are mounted,(under a right side CD sized cover) locate and disconnect a small 4 pin connector. Using a multi-meter set on OHMS and range of X 100 check between the BLUE and BLACK wires(#1 and #4 sparkplug wires) for between 360- 540 OHMS.

2.For #2 and #3 sparkplugs the wire colors will be YELLOW and RED, again 360-540 OHMS.

3.If the pickup coils are suspect of failing due to heat, they can be stressed using a hair dryer without the need of the engine running.

4.A replacement set of pickup coils might be obtained from a dealer who serviced the police Kawasaki’s.

5. If replacement pickup coils are not available, your next choice would be to order a Dyna “S” electronic ignition system from www.z1enterprises.com It replaces the IC igniter with a smaller module located where the mechanical ignition advancer was mounted.

6.Check the small 4 pin connector that the picup coils connect to for corrosion.

The IC Igniter(actually it gives the ignition coils their ground firing the coils)may also be failing.

The member Loudhvx has made a replacement using off the shelf GM modules:http://home.comcast.net/~loudgpz/GPZweb/Ignition/GPZgmHEImod.html

IC Igniter Replacements

The igniter from any of the following bikes is a direct fit replacement for yours.
KZ1000-J1 (1981)
KZ1000-J2 (1982)
KZ1000-J3 (1983)
KZ1000-K1 (LTD) (1981)
KZ1000-K2 (LTD) (1982)
KZ1000-M1 (CSR) (1981)
KZ1000-M2 (CSR) (1982)
KZ1000-P1 (Police 1000) (1982)
KZ1000-P2 (Police 1000) (1983)
KZ1000-P3 (Police 1000) (1984)
KZ1000-P4 (Police 1000) (1985)
KZ1000-P5 (Police 1000) (1986)
KZ1000-R1 (Eddie Lawson Replica) (1982)
KZ1000-R2 (Eddie Lawson Replica) (1983)
KZ1100-A1 (Shaft) (1981)
KZ1100-A2 (Shaft) (1982)
KZ1100-A3 (Shaft) (1983)
KZ1100-B1 (GPz) (1981)
KZ1100-B2 (GPz) (1982)
KZ1100-D1 (Spectre) (1982)
KZ1100-D2 (Spectre) (1983)
KZ1100-L1 (LTD Shaft) (1983)

Also, any igniter with one of the following part #'s will work since the original was superseded by these numbers.

21119-1356
21119-1041

badr0bot wrote:

OK my KZ1000 runs great for about 6 miles then starts to misfire and spit and sputter after she gets warm. It misfires at all rpms but almost dies at idle. Everything I've read says misfiring when hot is an ignition problem. .

Classic symptom of an old coil whose insulation flakes out when it gets hot.

Guess how I learned that.....:laugh:

Mine did exactly what you described.

Head gasket?
Have you checked the torque on all your head nuts?
I ask because I had similar issues years ago...

Have you done any engine work recently (head off)?

If not already done, would assure correct valve clearances.

Good Fortune!

bountyhunter wrote:

badr0bot wrote:

OK my KZ1000 runs great for about 6 miles then starts to misfire and spit and sputter after she gets warm. It misfires at all rpms but almost dies at idle. Everything I've read says misfiring when hot is an ignition problem. .

Classic symptom of an old coil whose insulation flakes out when it gets hot.

Guess how I learned that.....:laugh:

Mine did exactly what you described.

If a coil were going bad when its hot shouldn't that show up on the resistance test?

badr0bot wrote:

If a coil were going bad when its hot shouldn't that show up on the resistance test?

Nope. The insulation between the high voltage windings gets flaky and you start getting arc over. Resistance test can't see it unless you have an actual high voltage test instrument.

bountyhunter wrote:

badr0bot wrote:

If a coil were going bad when its hot shouldn't that show up on the resistance test?

Nope. The insulation between the high voltage windings gets flaky and you start getting arc over. Resistance test can't see it unless you have an actual high voltage test instrument.

OK then. Thanks Bountyhunter. That's what I needed to know.

badr0bot wrote:

bountyhunter wrote:

badr0bot wrote:

If a coil were going bad when its hot shouldn't that show up on the resistance test?

Nope. The insulation between the high voltage windings gets flaky and you start getting arc over. Resistance test can't see it unless you have an actual high voltage test instrument.

OK then. Thanks Bountyhunter. That's what I needed to know.

Considering Z1 now sells OEM type four Ohm replacement coils for $36, any old coil should get pitched. When my first coil flaked out, I got a "good" used one off ebay and paid about $30. Got about a year out of it until it went bad too. 30 year old coils are not worth the pain....:laugh:

Ignition coils are not located in the best area for cooling,added to this is extended engine running with no air movement at traffic lights and you have all the makings of cooking them.