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TOPIC: KZ400 won't start after rebuild

KZ400 won't start after rebuild 07 Jan 2019 17:11 #796368

  • OldguyJoe
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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
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.

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KZ400 won't start after rebuild 07 Jan 2019 17:21 #796370

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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.


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2002 ZRX1200R
81 GPz1100
79 KZ1000st daily ride
79 KZ1000mk2 prodject
78 KZ650sr
78 KZ650b
81 KZ750e
80 KZ750ltd
77 KZ400/440 cafe project
76 KZ400/440 Fuel Injected

www.dotheton.com/forum/index.php?topic=39120.0


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KZ400 won't start after rebuild 07 Jan 2019 17:31 #796371

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Thanks Rex. Good strong spark and compression. I feel like I'm missing something subtle.
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.

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KZ400 won't start after rebuild 08 Jan 2019 08:01 #796395

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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
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KZ400 won't start after rebuild 08 Jan 2019 09:13 #796403

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Have you checked coil wiring? Do you have them backwards?
I ride Z1's. I have a couple of '75's, plus an '80 KZ1000LTD. My lovely Sweetums rids a 1981 KZ550.

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KZ400 won't start after rebuild 08 Jan 2019 09:17 #796404

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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.
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Last edit: by loudhvx.

KZ400 won't start after rebuild 08 Jan 2019 10:57 #796408

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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
1980 kz750E1, Delkevic exhaust

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KZ400 won't start after rebuild 08 Jan 2019 15:19 #796417

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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.
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.
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KZ400 won't start after rebuild 08 Jan 2019 16:06 #796421

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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.

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KZ400 won't start after rebuild 08 Jan 2019 16:19 #796422

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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.
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.

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KZ400 won't start after rebuild 08 Jan 2019 20:05 #796429

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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.
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KZ400 won't start after rebuild 09 Jan 2019 17:25 #796458

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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.
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.

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KZ400 won't start after rebuild 09 Jan 2019 19:54 #796462

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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.

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Last edit: by loudhvx.

KZ400 won't start after rebuild 10 Jan 2019 16:44 #796499

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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.
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.

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KZ400 won't start after rebuild 10 Jan 2019 20:05 #796508

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KZ400s and KZ440s use the same ignition advancer.


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2002 ZRX1200R
81 GPz1100
79 KZ1000st daily ride
79 KZ1000mk2 prodject
78 KZ650sr
78 KZ650b
81 KZ750e
80 KZ750ltd
77 KZ400/440 cafe project
76 KZ400/440 Fuel Injected

www.dotheton.com/forum/index.php?topic=39120.0


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KZ400 won't start after rebuild 11 Jan 2019 07:45 #796519

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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.

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KZ400 won't start after rebuild 11 Jan 2019 17:48 #796555

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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.
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.

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KZ400 won't start after rebuild 12 Jan 2019 08:59 #796587

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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.

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KZ400 won't start after rebuild 12 Jan 2019 11:36 #796599

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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.
1977 weird Canadian version of KZ400.
Had a 1973 Kawi 175 in the 80s.

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Last edit: by OldguyJoe. Reason: additional info

KZ400 won't start after rebuild 12 Jan 2019 13:40 #796604

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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
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