KZ400 won't start after rebuild

OldguyJoe wrote: Spent some time on my knees this evening inspecting the timing marks and engine rotation.
All is as you say, hvx, except the rotor pointer is just above the pickup pole when F is at the fixed pointer.
Does this indicate I need to slightly advance or retard the ignition? It seems a hair's breadth difference, but could this be why it's not firing at all except when reversed 180° and backfiring?
Weird. It ran so well. Kicking myself for not noting timing marks before the rebuild.

No, I think the mark being a bit off is just a tuning issue for you to figure out later on when you find out why it won't start. There's a slight chance the timing is different because the advancer came from a 750 twin, maybe. I'm not sure if a 440 twin might also have different timing than a 400.

The non-start is puzzling. Does it even backfire (when the rotor is not 180 out)? With good spark I would expect it to at least make some sort of bang after a while.


Since you already did a top-end job I assume you may have done the following, so sorry if it's been covered, but just in case....
When you check for TDC or BDC are you using a feeler in the piston hole, or relying on the advancer? I don't think I would trust the advancer without knowing if the marks are the same as would be on a 400. Maybe 750 and 440 twin's marks are the same as your 400, but I wouldn't assume that.

It may even be possible, but I'm not sure, that the rotor was installed on your actual Kz400 points advancer unit. In that case, I would expect the marks to align with the motor, but then the rotor might not align with the advancer.

I always confirm piston TDC using a feeler through the plug hole to see how far off the advancer marks are. The T mark is usually within a degree or two of actual TDC.
In your case, it could be further off if it came from another model.

Not even a backfire, cough, or sneeze. No exhaust puffs, and plugs smell like gas. I even tried spraying a bunch of Quik-start down the plug holes. It truly is baffling.
I didn't use a feeler in the cylinder head, just a flashlight and my Mark I eyes. The advancer T mark aligns with actual TDC.
Thanks for putting your experience up against this. I'm at loggerheads here.

KZ400s and KZ440s use the same ignition advancer.


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Well, since you have spark, and have tried starting fluid, and there seems to be compression, and you've tried both positions of the rotor, and the timing marks seems to be close enough that they should work, I guess we have no choice but to go into those extremely rare situations where you have to start looking into very unlikely reasons for not starting. I don't like doing that because it is often something much more basic... but here goes...

To test for spark, you don't have to necessarily turn the crankshaft. You can gently tap a screwdriver to the center-pole of the pickup. It won't spark with every tap, but about 50% to 75% of the taps will create a spark when the plugs are in open air. It might be able to create as an intensive spark as turning the crank, and it might not be able to create a very long distance spark, but it will show sparks at the plugs. Remember, both plugs fire at the same time so both plug wires must have a path to each other or some common piece of metal. This tapping test might not work to check for long sparks as described below.

When some people test for spark, they only look at one plug wire and unintentionally leave the other plug wire unconnected and unable to complete a spark path. This will eventually damage a coil or igniter.

So one way a coil or igniter can fail is gradually. This means it may produce spark in open air, but under compression, the spark fails to occur at the plug.

The igniter can have a weak transistor which cannot stop the primary current above the required reverse voltage. When an igniter tries to stop the primary current in order to cause a spark, the coil produces a large voltage in the range of 300 to 600 volts depending on the plug gap and amount of fuel/air being compressed. If the igniter's transistor can only hold back 200v, then the spark might be good in open air, but under compression there will be no spark. The spark energy of the coil will be dissipated in the igniter and coil instead of at the spark plug.

A coil can have a similar symptom in that the insulator on the secondary side might have a weak spot. Under low-stress conditions like when the plug is in open air, the coil can deliver enough voltage to the plug to create a spark. But under high-stress conditions, inside the cylinder, the spark will jump internally inside the coil, through the weak spot in the insulation. If the coil is old and shows visible cracks, it will be a matter of time before it fails... usually after a hard rain.

The way to test for this is to see how far the spark can jump. When you test for spark, you are testing the current path from one plug wire to the other on the given coil. The spark path does not have to necessarily go to the engine block, but the engine block simply acts as an intermediate conductor for the two plugs. So you can just route one plug wire to the other to check for spark if you are using a bench test or if you want the plug wires placed more conveniently to look for spark. You can use two plugs installed in the plug wires, and then control the distance between the two plug bodies.

Never try to get a gap larger than 3/4". That will eventually damage a coil or igniter. But a good coil and igniter should be able to create a 1/2" spark without much trouble. 1/2" is usually enough to run any stock motor, and is certainly enough to start a stock motor. It's very easy to accidentally go larger than 3/4" and damage a coil or igniter so be careful. A bad plug can also cause troubles, especially resistor plugs. They can essentially become an insulator which will also damage the coil or igniter. Look to see if you see spark traveling along the outside of a spark plug. that indicates a bad plug.

When everything is assembled and you are trying to start the motor, if you hear a very clear and loud audible tick for every spark, it may be that the spark is arcing somewhere it shouldn't be. Usually you won't hear normal sparking events while starting the motor because of other sounds and the sparks are happening inside the engine. If you are hearing the sparks, the sparks might be leaking from the plug wires to the head or elsewhere to some other metal.

Seriously, you'll have to send me an invoice for all your help here.

Using your suggested test, I got just barely 1/2" of spark between the plug bodies. The pickup-tap method didn't cut the mustard, so I had to kick it over.
I guess this calls for a new coil and igniter, since it wouldn't get past 1/2". So weird that it started right up before the rebuild. Now it doesn't even sneeze with quik-start shot right down the plug holes. As you said earlier, it should at least be coughing. Also, there was no snapping sounds of spark anywhere while turning it over.
Only explanation left is coil and igniter? I have the Dyna 2.2 ohm coil in my Z1 shopping cart. Is there any sense in trying new plugs as a cheap thing to try? There was no spark along the plug body.

Always try cheap simple stuff first. Half inch spark should be enough to start the bike easily. So its not likely the coil or igniter is preventing startup. Plugs would be a definite first choice for me. For some reason I assumed they were new, but that is probably my senility kicking in.

Later on, it may be good to look at a coil replacement if the original is known to be 25 years or older.

The plugs looked fairly new, but I tried a new set anyway. Still barely getting 1/2" spark between plug bodies. Next thing to try is the new 2.2 ῼ Dyna coil on order from this site's advertiser, Z1. This coil is undoubtedly original, 42 years old.
After that, igniter. I'll search for testing techniques for the igniter while I'm waiting for the coil to arrive. Pickup resistance is 500 ῼ. High? Low?
Further updates as events warrant.
Thanks again for all the help.

OldguyJoe wrote

Pickup resistance is 500 ῼ. High? Low?

From the KZ440 service manual



There is a 440 Service Manual available here on KZR - see the drop down menu at "Articles" above.

The supplement at about page 270 has some good info on the 440 ignition system which you might want to check . Something in it might jump out

Cool, thank you JR. That's more in-depth than the service manual I have.
Igniter bench-test ohmmeter numbers are low, according to the charts in the 440 manual, plus some numbers are reversed. It could be a publishing error, or my igniter is buzzed.

Ohm tests on the igniter tend to be very unreliable. Manufacturers can change the specs without notifying anyone. Also, when using an ohm-meter to measure active devices, the internal construction of the meter will alter the results. Ohm-meters are really only reliable at measuring resistors. Things like diodes and transistors are not really ohm-meter friendly.

You can test the ignition coil with a DMM.

Is the battery fully charged? MyZ1 will not run with a dead battery.

Yes it is. I'm keeping it on a low-C maintenance charge.
Glad to hear I can wait on replacing the igniter till after I try the new coil. Test procedure in the manual was thorough, noting ῼ readings in both polarities.
Would it be of help to find someone with a document scanner and upload my service manual to the articles section? Maybe the office supply store has that service.