TOPIC:

On my 1979 KZ1000 (engine is not stock though, it has the newer ignition, not points) whenever I hit around 7,500 rpm, the engine starts misfiring. If I hold the throttle wide open, after a few seconds the misfiring stops and the engine revs to redline.

I am pretty sure it's not the carbs, definitely not a rich misfire, I have tried many possible main jet/needle combinations. Carbs are VM 26 pumpers, running 117.5 mains, needle in richest position, V&H 4in1, K&N filters.

Assuming it's not the carbs, what should I be looking at to rule out ignition problems? The advancer works correctly (checked with the light), however I am not quite sure what to look at next. Could the coils be the problem? Don't know too much about ignition, so any advice would help!

Thanks a lot!

Make sure the weights on the mechanical advance unit are not sticking and that the springs are not weak or broken. Either of those things could cause issue at hi rpm.

I am pretty sure the advancer mechanism is ok. With the light connected I revved the engine up and the ignition advanced correctly. When going off the throttle, it did not stick or anything but returned immediately.

Might check your coils for any damage... crack in the main housing, where they bolt up and the wiring in that same area?

Just from a visual inspection they look ok.. Can someone tell me, is there anything I should measure, resistance of the wires, voltage at the coils (at different rpms?), etc.

Stock ignition coils? If it were me, I'd replace the coils, sparkplug wires, and run them with no resistance in the sparkplug caps. Dyna sells Copper sparkplug wires, with molded on rubber boots, available through Z1 enterprises.

The stock coils have 1/4" push on electrical connectors, the aftermarket Dyna and Accel use ring terminals, so if you upgrade, keep that in mind.

Some information:
Ignition Coil Primary And Secondary Wiring

Ignition coils on the 80’s Kz1000,Kz1100’s and Gpz1100’s are wired the same, that is as you sit on the bike, the LEFT ignition coil primary(small wires) are two wires, RED and BLACK. The secondary (or sparkplug wires) go to #1 and #4 sparkplugs(your primary wiring may be different).

Read carefully, as the 550’s, 650’s, 700’s & 750’s are backwards to what is listed for the bigger 4’s.

The cylinders are numbered left to right as you sit on the seat; #1,#2,#3, and #4.

For the RIGHT ignition coil, the primary wires, again are two wires, RED and GREEN, with the secondary going to #2 and #3.

The RED wire gets it’s voltage from the run/stop switch on the right handlebar switch pod. Your primary wiring may have a different color.

The BLACK and GREEN wires connect to the IC Igniter(if the bike has the Kawasaki supplied electronic ignition) it actually gives the coils their grounds to fire the sparkplugs. The RED wire is common to both ignition coils.

Primary(small wires) side of the coils will read between 1.8 to 3.0 ohms.

Secondary(sparkplug wire ports)side of the coil will read between 10.4K to 15.6K ohms. These ports are wired together, so it makes no difference which is used, as long as the correct coil to sparkplug configuration is followed.

The sparkplug caps should read 5K OHMS(5000), any higher, or a reading of infinity means new caps should be ordered. When re-installing the old or new sparkplug caps, cut about ¼” off the sparkplug wires for a new un-corroded connection.

Never run supression sparkplug wires with sparkplug caps containing the 5000 ohm resistor, as now there will be two (2) resistances in the ignition coil’s secondary circuit, causing weak and intermittent spark.


To stress the ignition coils, take a hair dryer, heat the coils and see if the ohm readings change from cold to hot . If they do, it’s time to buy new coils.

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Keep in mind, the wiring is reversed for the 550’s, 650‘s,700’s, and 750‘s, that is the RIGHT coil primary will be two wires, RED and BLACK with the secondary(sparkplugs) going to #1 and #4.

The LEFT coils primary wiring would be again two wires, RED and GREEN, with the secondary(sparkplugs) going to #2 and #3.

An indication of black and sooty sparkplugs may not mean a carb or carbs are in need of cleaning, but may mean the input voltage is low.

When checking the input voltage to the ignition coils, first have a fully charged battery, and the using a multimeter, set it up to measure VDC(Volts, Direct Current), range of 20.

Put the RED probe from the multimeter on the same terminal that either a RED wire or ones that’s RED with YELLOW stripe, and the BLACK probe on either a good frame/Earth ground or the battery Negative(-) terminal/post.

Depending on the motorcycles current draw( lighting, and other high amp needs) the reading might be 10 volts or more, but if the reading is down around 8 volts or less, this indicates a corrosion or wiring problem needs correcting to improve input voltage to the coils.

These engines have what is known as a “Wasted Spark” that is, a sparkplug will fire during an exhaust stroke. It does no damage and many other motorcycle engines have this design.

Ignition Coils And Sparkplug Wire Choices
What came with the bike were ignition coils that even when new were marginal, add years of cooking under the tank in stop and go traffic, and the coils will fail when hot.

Replacement coils can be bought at www.z1enterprises.com. I believe "Emgo" is the brand. They also carry the popular Dyna 2.2 and 3 ohm coils along with replacement sparkplug wires.

Now, you have a choice on sparkplug wires:
1. Copper plug wires with no supression caps(the best choice, will produce greater spark, but will produce audio noise on Radio's & T.V.'s)

2. Copper plug wires with supression caps(a built in 5000 ohm resistor, that can some times fail, like what came with the bike).

3. Copper plug wires with no supression caps, but using resistor plugs(the "R" in the plug number, like B8RES).

4. Supression plug wires with no supression caps.

NEVER use resistor plugs and supression caps or supression plug wires, as now there will be two (2) sources of resistance in the secondary loop of the ignition coils, greatly reducing the spark energy.

Another choice is the Accel 3 ohm coils, with a similar primary(small wire) electrical connection using ring terminals as the Dyna ignition coils. Whatever brand of coil you go with, make sure the primary wires will clear the mounting hardware, as the spacers will come really close, possibly causing an electrical short, blowing fuses. Some riders have replaced the metal spacers with Nylon or Plastic non conductive ones, reducing the chance of an electrical problem.

anotherZ wrote: ...1979 KZ1000...whenever I hit around 7,500 rpm, the engine starts misfiring. If I hold the throttle wide open, after a few seconds the misfiring stops and the engine revs to redline...needle in richest position....

Would return jet needle clips to middle position, and test ride.

Am thinking the "richest position" may be loading up the combustion chambers with excessively rich mixture until it gets blown out after a few seconds at wot where the jet needle position is irrelevant.

Good Fortune!

anotherZ wrote: Just from a visual inspection they look ok.. Can someone tell me, is there anything I should measure, resistance of the wires, voltage at the coils (at different rpms?), etc.

Does the bike have the original stock coils? If so, they are 35 years old, old, old.
A simple test is to ride the bike at highway speeds, then stop & feel the coils --- press hard w your fingers. They should be warm, not hot.

Also, make sure the battery is good. If it's a wet cell type, check the electrolyte level.
Battery problems have caused my bike to run poorly at higher rpms a couple of times.

Thanks a lot everyone, good advice! Heading out for a ride now and will look under the tank later. You definitely gave me a good list of things to look at!

anotherZ wrote: ...1979 KZ1000...whenever I hit around 7,500 rpm, the engine starts misfiring. If I hold the throttle wide open, after a few seconds the misfiring stops and the engine revs to redline...needle in richest position....

Could test mid-throttle mixture being provided by jet needle clip position by riding a few miles at the 7500 rpm while the engine is misfiring, and then simultaneously chop the throttle and switch off the ignition (or hit the kill switch) and coast to a stop.

Then read the plugs at roadside. Likely find them ultra sooty from excessively rich mixture at this throttle position where the jet needle clip position is influential.

Do another test ride and repeat the throttle chop procedure from WOT. Again read the plugs at roadside. Likely find them less sooty and evidencing a better air/fuel mixture produced by the WOT position where the jet needle clip position is irrelevant and the mixture is dependent on size of the main jet.

Imo, having the jet needle in its richest position is ill-advised (and rarely necessary).

Tip -- carry along a short section of hose that fits snugly onto a spark plug, and use it to extract the hot plugs at roadside without burning fingers.

Good Fortune!

And regardless of mixture, it's always desirable that the ignition system produce properly timed fat blue sparks. This may be tested by removing the plugs and observing the spark quality while spinning over the engine.

Even with perfect carbs, perfect fuel supply, and perfect compression, insufficient spark quality can result in sooty plugs.

Good Fortune!