KZ400 won't start after rebuild

Hi guys. I've got a real head-scratcher here.
Bought this 1977 KZ400 as a winter project with my son. First bike since the eighties for me.
The biggest mess was the wiring, so I rewired from scratch, to legal minimums, using several wiring diagrams. The bike is a weird Canadian version that combines elements from several models, eg. transistor ignition rather than CDI.
After the re-wire, she fired up on the second kick. I couldn't believe it, as it hasn't run in years. After a few minutes, the left cylinder overheated. Oh well, it's a planned top-end rebuild anyway.
Pre-rebuild compression numbers are as follows:

Dry
right-140
left-115 (yikes!)
Wet
right-140
left-160

Left carb had dead flies in the float bowl, so that was a gimme. Soaked all carb parts in cleaner, and flow now seems free.
Cylinder walls were pretty glazed, so I honed them out to a nice crass-hatch pattern. Piston rings looked new, but valves on left head looked over-heated. Easy job to lap them back in nice and tight.

Now here's the catch: after reassembly with shiny new gaskets, the darn thing won't fire. Good strong spark, and compression now is:

Dry
right-152
left-138
Wet
right-190
left-170.

Finally, there's plenty of gas getting to the cylinders.

So, am I missing something with the timing? Some inside secret like it should be advanced or retarded a bit? I set it up according to the workshop manual. I even pulled the head back off to check that the T marks are perfect. I guess I should have checked original timing positions before disassembly.

Looking for something I may have missed here, guys. It ran great before the rebuild, except for the overheat.
Thank you for reading, and for the years of posts that I used thoroughly during this job.
Joe

OldguyJoe wrote: Hi guys. I've got a real head-scratcher here.
Bought this 1977 KZ400 as a winter project with my son. First bike since the eighties for me.
The biggest mess was the wiring, so I rewired from scratch, to legal minimums, using several wiring diagrams. The bike is a weird Canadian version that combines elements from several models, eg. transistor ignition rather than CDI.
After the re-wire, she fired up on the second kick. I couldn't believe it, as it hasn't run in years. After a few minutes, the left cylinder overheated. Oh well, it's a planned top-end rebuild anyway.
Pre-rebuild compression numbers are as follows:

Dry
right-140
left-115 (yikes!)
Wet
right-140
left-160

Left carb had dead flies in the float bowl, so that was a gimme. Soaked all carb parts in cleaner, and flow now seems free.
Cylinder walls were pretty glazed, so I honed them out to a nice crass-hatch pattern. Piston rings looked new, but valves on left head looked over-heated. Easy job to lap them back in nice and tight.

Now here's the catch: after reassembly with shiny new gaskets, the darn thing won't fire. Good strong spark, and compression now is:

Dry
right-152
left-138
Wet
right-190
left-170.

Finally, there's plenty of gas getting to the cylinders.

So, am I missing something with the timing? Some inside secret like it should be advanced or retarded a bit? I set it up according to the workshop manual. I even pulled the head back off to check that the T marks are perfect. I guess I should have checked original timing positions before disassembly.

Looking for something I may have missed here, guys. It ran great before the rebuild, except for the overheat.
Thank you for reading, and for the years of posts that I used thoroughly during this job.
Joe

All KZ400s had points.
Start with the basics. Compression, fuel and spark.
Pull the spark plugs and see if you are getting spark.


.

Thanks Rex. Good strong spark and compression. I feel like I'm missing something subtle.

I know very little about the 400s so just a few shots in the dark here

You got compression so good job on the valves and hone

You got gas but is it the correct air gas/ ratio ? i.e. do you have an airbox hooked up ?

You have good spark but is it happening at the right time ?

Like Nebr_Rex said all the 400s had points as did the 440s for first year or so. Later 440s had factory electronic which is reportedly better than CDI . You mention having a transistorised ignition. Is it an aftermarket system? Can you post a photo showing whats under the ignition cover on the right hand side ?
Did you remove the timing advancer at any time and possibly reassemble it so that the spark happens 180 degrees out? i.e. at BDC. . I dont know if both pistons are at TDC at the same time so this might not make any difference on the 400.

As the crank rotates (backwards on the KZ twins) spark should happen as the F mark on the advancer aligns with the fixed mark. On a points system you can rig a 12V bulb or test light between points and ground and watch the bulb light up as the marks align. You might be able to use a multimeter with your electronic ignition..

A long time ago I did a top end on a Honda CB250. Put it all back together and it just would not fire. Took me about a week to realise that that I had the wires to the coils (the Honda had 2 coils) reversed.

As you say probably something simple

Good Luck

Have you checked coil wiring? Do you have them backwards?

400/440 motors have 360-degree cranks, so both plugs fire at the same time. If the ignition rotor is 180 degrees out, then both cylinders will get spark at the wrong time. This usually leads to a a no-start, but with a very occasional backfire.

And yes, a photo would be nice to help determine what's going on with the ignition. Very very few Kz's had actual CDI, it was usually the smallest of the Kz's (smaller than 400). Factory and aftermarket were most often transistorized Kettering ignitions. There are very few aftermarket bolt-on ignitions for Kz400's and the 440 electronic ignitions are not super common to see on 400's, so it's sort of a toss-up on what you have.

hardrockminer wrote: Have you checked coil wiring? Do you have them backwards?

As far as I can see from a quick look at parts diagrams the 400 and 440s should have only one coil............... unless his current odd ball ignition uses 2

Thanks for the ideas guys.
I did occur to me that the timing advancer may have been in backwards, so I flipped it 180°. Engine then began sparking at BDC and spat smoke out the carbs, Good call on that one, loudhvx.
JR, yes indeed this bike has the one coil and I made sure to to get them on the right plugs. Further, the F mark on my advancer indeed aligns just before pistons reach TDC.
Here is a pic under the cap. The transistor module is up by the coil.

When the advancer F mark is at the pointer, the iron rotor's point should be near the center of the pickup. If it's opposite, then the rotor is 180 out.

That is a factory ignition for Kz440 and 750 twins. That should work with your Kz400 motor, but you will want a coil from one of those later models, or a new replacement. Dyna makes a gray, 2.2 ohm coil which should work well. 3 ohm coils should also work fine.

A points coil should still fire and work for idle and puttering , but you will want a coil in the 2.2 to 3 ohm range to work with that ignition.

Good lead there, hvx.
This coil reads 2.7 ohm. So it should be fine then? Before the rebuild, the motor seemed to rev up a-ok.
When the advancer F is at the fixed timing point, the iron rotor's point is just above the pickup, and the pistons are just reaching TDC.

When the F mark lines up, the point of the rotor should be at or just below the center pole of the pickup. The crank, when looking at the ignition side, is rotating CCW. The spark fires just barely after the rotor point passes the pickup center, which would be just CCW of the pickup, or in other words, just below the pickup center.

The pistons should not be near TDC yet when the F mark lines up. They should be at TDC when the T mark lines up with the fixed pointer.

As you said, the coil should be fine assuming it is fully functional.

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.