TOPIC:

Hello, I'll try to keep this short and sweet and appreciate any thoughts.

I bought a 1981 Kz750 Ltd at the start of the year after passing my test which initially ran fine until it started cutting out, mostly when coming to a stop. I am new to riding, motorbikes, tinkering, etc but have been trying to solve my many problems through these forums and youtube. I think a list of the chain of events may help:

Bike cut out, more frequently as time passed
Bike failed to start
Cleaned carbs
Bike ran but eventually died and didn't start. Made horrible noise when trying to start.
Replaced clutch starter rollers, pins, springs ( great learning curve for a novice)
New oil filter
Bike ran but still randomly cut out
Checked for air leaks
Carb floats adjusted
New fuel filter
New battery
New spark plugs
Tested compression 100, 110, 110, 95 (dubious cheap compression tester)
Bike died, fuse had blown, started again with new fuse but died a few miles down the road. New fuse, no difference
No spark on any plug
Two new coils, still no spark
Aaaaaaaaaaaaaaaggggggghhhhhh!!!!!!

I am loving riding, loving having a KZ750 LTD, loving tinkering but just need to get this beauty back on the road. Summer is pretty much here! As stated, I am a novice, this is all new to me but any help is much appreciated.

Check IC Igniter.

Condition of plug wires?

Good Fortune!

Bear with me if I get long winded here...
35+ years ago I was a newly trained electronics technician fixing Printed Circuit Boards (PCB). There were several other Techs and we all sat at a row of benches fixing PCB's. There was an "actions taken" form where you documented the symptoms and trouble shooting steps, along with any components replaced. In theory, another tech could use this form to pick up where you left off.
Now over in the corner was a stack of PCB's that were commonly refereed to as the BFH's (Boards From He11). These were boards that had been worked and reworked so many times that everyone had given up. The actions taken forms were 10 to 15 pages long and every component had been replaced at some point.
One day I took one of these BFH's and spent an hour stripping, cleaning and re-soldering every connection. I put it on the test fixture and got a big green "PASSED"! A BFH was moved to the good pile! I repeated this process, fixing probably 90% of the BFH's, some of which that had been there for years. I didn't tell any one what I was doing until I had completed the stack. Rumors began to circulate about the Young Genius Tech who slayed the BFH stack.
The point of this story is 90% of electrical problems (especially intermittent ones like you described) are due to corrosion or poor contacts. Your wiring is 35+ years old and has spent it's life in a harsh environment. Spend an afternoon and clean /inspect all the connectors on your bike. Get some electrical contact cleaner (Deoxit is a popular choice) and a fine wire brush or glass fiber pen. If the pins are deeply recessed and you can get to them, soak them with cleaner and remove/insert them several times. You may just slay your bike's BFH problem.

Good Luck

Thanks for the advice. The plug wires are good. The IC Igniter I did suspect but it sounds like I'll only find out if I buy a replacement. The connections I will clean and check.
I have tested the connector that goes to the pickup coils and the readings look good. The connector to the ignition coil, however, doesn't read anything when I test the ground wire (black/yellow). So, I assume there is a connection fault somewhere but I don't really know where to start. I don't know where that wire goes as everything is taped up.
Any words of wisdom greatly appreciated.

You need to have a wiring diagram for your bike, the 1980 KZ750 LTD also known as H1 is the same as the 1981 KZ750 LTD. also known as
H2, if you don't have the service manual, download the manual that is available here and follow the wires according to the diagram and I'm pretty sure you are going to find where the problem is, it can easily be a broken wire or bad connection..

If you go to the home page here and scroll down you will find a list of shop manuals on the right hand side. Download the one listed as gpz 750 base manual as that will cover your model. The ignition section will have a trouble shooting flow chart. Wiring diagrams in manual are black and white and as suck not great. Use google to find a colour one.

You have already done some trouble shooting so you could continue by checking if there is power ( 12 volts) at the coils. Remove gss tank. Each coil will have a red wire and either a green or black wire connected. Red wire is power. With ignition switched on set your multi meter to 20 volts dc and put + probe on one red wire and - probe on frame or engine. What voltage are you seeing?

If zero voltage then power for the ignition goes from battery to fuse to ignition switch to kill switch to coil and fault is probably between ignition switch and coils.

If you have 12 volts at coil then problem is probably the signal . Green and or black wire , ignitor, pulse coils or the connectors in between.

The manual and colour wiring diagram will help you here.

Good luck
Edit . Looks like it took me 20 minutes to write that.

Thanks for your time. The test showed 12 volts so it appears to be the igniter or connectors. Does anyone know if an IC Igniter off a KZ 1100 Spectre is compatible with a KZ750 Ltd? The one I have seen looks identical, the wires, everything.

A quick look at kawasaki.com , owner info, parts diagrams shows ignitor part# 21119-1041 to be in common for for both 1981 kz750 LTD and 82 Spectre 1100

It's alive...........just!

So, I put a new connector with new pins on the wires going to the IC Igniter as it was corroded. The readings from both plugs to the igniter checked out so I assumed the igniter was faulty.

I replaced the igniter with one I found which looks identical but is from a KZ1100 Spectre. The part number on my dead one is 21119-1020, the replacement is 21119-104?. Not sure if this makes a difference. Anyway, the bike fired up but is running on cylinders 2 and 3 only. There is no spark at 1 and 4.

Both coils are new and primary readings are 3.6 ohm. The secondary readings are 16 kohm, with the caps on 27 ohm.

I tested both coils as suggested by JR and both read almost 12V.

As this is all new to me it's a bit of a guessing game but finding your input very helpful. So, guessing again, is it now likely to be a connection failure? Low compression?

When it does start up, there does seem to be a kind of knocking noise from the engine.

Apologies for my lack of knowledge.

Sounds like you are making progress

When it does start up, there does seem to be a kind of knocking noise from the engine.

Normal for a motor running on only 2 cylinders

Both coils are new and primary readings are 3.6 ohm. The secondary readings are 16 kohm, with the caps on 27 ohm.

Stock coils have lower primary resistance .



I have no idea what impact your 3.6 ohm coils may have on other components of your ignition system

Having said that you could try the following
Pull all 4 spark plugs and ground them on the engine while connected to their plug caps and plug wires. Hit the starter button. Have you spark on all 4 plugs including the 1 - 4 plugs ?
If yes then problem is valves compression or fuel/carbs.

If still no spark on 1-4 plugs then swap the black and green wires to the other coil. It does not matter if you swap the red wires to the other coil as these both carry battery voltage all the time ignition is on. it does matter which coil the green is connected to and which coil te blackis connected to. I just cant remember if green is for 1-4 and black is for 2-3 or vice versa.
In swapping wires you are trying to see if the problem follows the wires.
With black and green swapped hit the starter button again. Did the problem follow the colored wire to the 1 - 4 coil?
If no then problem is with plugs, plug caps, coil etc.
If yes then trace back that colored wire - Is there continuity (ohms) from wire at coil to connector at ignitor? Is there continuity from ignitor to the pick-up coil under the CD sized cover on the right hand end of the crank?
Crack open the manual and follow tests for ignitor and pick-up coil

Good luck
PS dont forget to swap back the coil wires to where they should be

Thanks again JR! Not quite there yet but you've really helped.

So I tried grounding all 4 spark plugs on the engine and to my surprise they all had a spark. I didn't expect it as I had grounded them individually about a thousand times, only getting a spark on 2 and 3. Is there a reason for this?

I tested the compression (cold test) again and my results were 110, 105, 110, 105

I have read that they should be higher than that but I'm not sure what a cold test should produce. But as the bike does run I'm assuming these results aren't too bad as they are all similar to each other.

With all pipes hot I thought Id take it for a quick test ride. I got about 50m down the road before it cut out.

So that leaves the carbs. I've taken them off again so I'll have a good look and check the float levels again.