1979 kz 750 twin no spark

Hello to the forum. I'm a newbie with the forum deal. I have a 79 kz750 (b4) with no spark on either plug. I had the coil tested and the mechanic said it was good. I cleaned the points and changed the condenser. I gapped the points at matchbook thickness (harley rider said it would get the bike running again). Checked the connectors (1 was broke, blue wire to points) fixed that. Still no spark. What could I be missing and where would I look? Been googleing (if thats even a word) for 4 days. Thank You for any help to have the wind in my hair again, before i rip it out!

B.J.

Welcome flyersfan0405.

There is a wiring diagram for the 79 750 twin in the file data base. At the green bar at the top of the page: KZ Information, File base, 1979, Kawasaki KZ 750 B4, Z750 B4.
The Canadian model diagram is the same as the U.S. model.

Assuming good battery,
Check for power to the coils, ignition on,12v power at the connector for the red/yellow wire from the coil.

If not, check connections from:
(assuming no rewire by a previous owner)
Battery to starter relay,
starter relay to red/white connector
(double plug - 1 to 20A fuse - 1 to regulator),
connector to 20A fuse, check fuse
20A fuse (white wire out) to connector in headlight bucket,
white wire connector to ignition switch (power in)
ignition on power out on yellow wire,
ignition yellow wire to connector,
yellow wire to kill switch (right hand control),
kill switch red/yellow wire out to a 4 pin connector,
4 pin connector red/yellow wire to connector (this is the one that the red/yellow wire from the coil plugs into)under tank.

Every connector and contact is a potential short.

If you do have 12V at the coil, and your coil,plugs, points and condensor are working, you should have spark.

As an additional note, the clutch lever that must be pulled in for the starter button to work.

Good Luck,
Jim

Thank you very much Jim. I'll print out the diagram and check all the connections and voltage tomorrow. I'll keep an update on what I find. Thanks again!

Ok here we go. I tested for power at the coil with the ignition on, on the yellow/red wire. I have 11.90v on the wire. Grounded out the plugs on motor and still no spark across the gap, not even a faint spark. Is the problem with the coil even though a mechanic said it tested good?

With all wiring removed from the igntion coil, what does the primary side ohm out at(where the small wires went)?

Check the sparkplug ports too for ohm readings.

Primary(small wires) side of the coil 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.

If readings are good with ignition coil cool, stress it with a hair dryer and check again.

I believe www.z1enterprises.com can get you a new ignition coil.

thanks mfolks. tested the small wires and got 5.4 ohm across. spark plugs spiked to 20k ohm. tried testing again to make sure and getting nothing. good guess that its the coil? BTW the bike was running earlier. can a coil just go bad without warning?

Where ignition coils are mounted, it makes for poor air flow cooling. Under the tank traps the engine heat, add a long time stuck in slow moving traffic and the recipe for coil failure.

Your coil is probably the one that came with the bike, and yes, they can develop an internal problem and fail with little to no warning especially if you have had the bike for a number of years.

If the input voltage is there, and then the process of elimination says the ignition coil is the prime suspect ruling out the points,condensors,sparkplug caps, and related wiring.

Motorcycle electrical troubleshooting can be a logical process, requiring tools,some note pads,writing instruments, and the bikes wiring diagram.

I like using a self powered test light for simple switch continuity checks, and either an analog or digital mutimeter for current and voltage testings

Thanks MFolks. I've worked on cars and finding out the hard way that bike are a completely diffrent animal. looks like z1 is going to get my patronage since everything seems to be discontinued except the spark plugs (thank god for some aftermarket). I appreciate your help and I'll keep everyone updated. Thanks again!

P.S. this is the first bike I've owned and ever worked on so all of everyones knowledge is very helpful.

This website has some very technical members(I can't remember at the moment how many), so don't be afraid to ask questions.

Myself, I love a good motorcycle electrical mystery.

flyersfan0405 wrote:

thanks mfolks. tested the small wires and got 5.4 ohm across. spark plugs spiked to 20k ohm. tried testing again to make sure and getting nothing. good guess that its the coil? BTW the bike was running earlier. can a coil just go bad without warning?

Yes, coils go bad without warning. Some will also Ohm good and then fail under load when the high voltage arcs down.

My 1979 KZ750 B4 coil gave me such a ration of grief, I wasted a lot of time on it. Z1 sells a direct replacement (four Ohm OEM type) coil for $36. Punt the old one.

flyersfan0405 wrote:

Ok here we go. I tested for power at the coil with the ignition on, on the yellow/red wire. I have 11.90v on the wire. Grounded out the plugs on motor and still no spark across the gap, not even a faint spark. Is the problem with the coil even though a mechanic said it tested good?

You need to verify the 11.9V (steady) at the yel-red wire, and then check the blue wire. It should read 11.9V with the points OPEN, and it should read 0V with the points closed.

That verified, the only other thing that can cause the spark to go away is a bad condenser.

If it was my bike, I would get a new coil and also points/condenser and then not have the problem again.