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KZ440 Won't Start After Top End Rebuild 23 Jan 2019 19:21 #797393

  • Jaytraeg
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Hey all, here's the story so far:

My bike (1981 KZ440 LTD) was burning oil, so I took off the head and cylinder block to see what was going on. On inspection, the piston rings looked fine, the cylinders were a little glazed, and the valve stem seals looked fine. I had the cylinders honed, reused the rings, replaced the valve stem seals and all gaskets that were taken off with new ones. I made sure the bore and roundness were both in usable range, and reassembled completely according to the manual found on this website. Now, the bike won't start at all! It cranks, but no popping/banging/coughing like it even wants to start, even with starting fluid right in the cylinders.

Things to note:
-I didn't mess with the timing advancer except for setting the cylinders to TDC
-Valves were gapped to spec after reassembly
-Spark is good and strong
-Plugs are wet/smell like gas
-Oil was changed after rebuild
-Tried switching plug wires, but no change
-Battery was charged to full juice and is in good condition
-Gas is fresh, and carbs have gas in the bowls (plus were cleaned very thoroughly during the rebuild process)
-Looking in the spark plug holes while cranking, the valves are opening and closing smoothly

I'm stumped! Any ideas?
1981 KZ440 LTD

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KZ440 Won't Start After Top End Rebuild 24 Jan 2019 00:52 #797411

  • Nebr_Rex
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What is your cranking compression?
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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KZ440 Won't Start After Top End Rebuild 24 Jan 2019 12:06 #797439

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I don't know, haven't checked it yet. My compression tester is in another city at the moment (I'm at school), but the next time I go up I'll make sure to grab it. Anything else I can look for in the mean time?
1981 KZ440 LTD

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KZ440 Won't Start After Top End Rebuild 24 Jan 2019 18:04 #797447

  • baldy110
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Pull a plug out use your finger to plug the sparkplug hole. Open the throttle all the way. If you can't keep your finger on the hole while cranking then you have enough compression to start it.

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KZ440 Won't Start After Top End Rebuild 25 Jan 2019 11:34 #797493

  • loudhvx
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There could be something in this thread below, coincidentally very similar situation.
www.kzrider.com/forum/2-engine/609860-kz...fter-rebuild?start=0

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Last edit: by loudhvx.

KZ440 Won't Start After Top End Rebuild 25 Jan 2019 12:45 #797498

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Thanks for the suggestion, baldy, I'll give it a go. I'm pretty sure the compression should be at least enough to get the darn thing to give me something. And thanks for the link to that other thread, loudhvx! I couldn't really follow a lot of the jargon about timing, but it seems like my bike is acting very similarly to the OP of that thread. How would I go about checking if my timing is off? Like I said, I didn't mess with the advancer during the rebuild and I triple checked that the cam was timed correctly according to the manual, but it sounds like it might have gotten 180 degrees off somehow? Thanks for the help all.
1981 KZ440 LTD

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KZ440 Won't Start After Top End Rebuild 25 Jan 2019 20:12 #797529

  • OldguyJoe
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Hi Jay.
OP of the other thread here.
I just tonight found time to install the new coil, but the kids are sleeping and it's -11° outside, so a test run has to wait till morning.
Will gladly update you on the results.
Further, if you didn't remove the advancer or timing rotor during the rebuild, you don't have to worry about the 180° reversal thing.
Joe
1977 weird Canadian version of KZ400-s3
Had a 1973 Kawi 175 F3 trail bike in the 80s.

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KZ440 Won't Start After Top End Rebuild 26 Jan 2019 12:55 #797567

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My engine started up with the new coil.
Who knows what went wrong with the old one, as the engine ran great before the rebuild. Perhaps it had just enough oomph to spark with low compression.
Anyhow, I had good luck ordering the coil from this site's advertiser. I don't know which one you'd need, but surely someone here does.
Best of luck.
1977 weird Canadian version of KZ400-s3
Had a 1973 Kawi 175 F3 trail bike in the 80s.

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Last edit: by loudhvx.

KZ440 Won't Start After Top End Rebuild 26 Jan 2019 13:09 #797572

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Thanks for the update Joe. 30+ year old coils are the only thing that ever got me stranded, so I usually don't trust them even if they pass a spark test, like yours did. I just hate to tell someone to spend money and not have that fix the problem. I'm glad it did in your case.

Jaytraeg's bike would use the same coil as you since you probably have a 440 or 750 twin ignition.

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KZ440 Won't Start After Top End Rebuild 26 Jan 2019 13:11 #797573

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I'm happy to hear that, Joe. Congratulations on your new working motorcycle!
Now I forget, did you say that your old coil still had an ohm reading that was considered within spec according to the manual? If so, how did you go about diagnosing the coil as faulty? That part of the thread was a little confusing to me.
In an case, looks like I'm going to spend part of the evening doing a resistance check on my coil. Thanks for the leads, guys!
1981 KZ440 LTD

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Last edit: by Jaytraeg.

KZ440 Won't Start After Top End Rebuild 26 Jan 2019 16:40 #797604

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Jaytraeg wrote: I'm happy to hear that, Joe. Congratulations on your new working motorcycle!
Now I forget, did you say that your old coil still had an ohm reading that was considered within spec according to the manual? If so, how did you go about diagnosing the coil as faulty? That part of the thread was a little confusing to me.
In an case, looks like I'm going to spend part of the evening doing a resistance check on my coil. Thanks for the leads, guys!


I don't mean to answer for Joe, as he is perfectly capable, but as I understand it, he was getting good spark at the plugs in open air tests whenever he was kicking the motor over. But when he was doing long-spark tests by placing the plug bodies about 1/2" apart, he was just barely able to get spark. That does indicate a weakness in the coil or igniter (coil is more likely to fail), but it should have still been enough to start a normal motor, especially on ether. Perhaps it was a combination of a weak coil and low compression making it difficult to start?

I normally spray ether into the carbs so the ether only gets carried in with air, and is atomized.
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Last edit: by loudhvx.

KZ440 Won't Start After Top End Rebuild 26 Jan 2019 20:55 #797655

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Alright, I ran a few tests and this is what I found out.:
The primary winding resistance (resistance between the two power terminals on the coil) measured at 2.0 ohms, which is out of the usable range specified in the service manual (3.2-4.8 ohms)
The secondary winding resistance (resistance between the two spark plug wires) measured at 11.3k ohms, which is in range of the 10.4k-15.6k ohm usable limit.
I think this is enough to condemn the coil, so I'll get a new one ordered. On the Z1 website, it says that using a coil with a slightly higher resistance is better than using one of slightly lower resistance (which I'm assuming is referring to the spec for the primary winding resistance listed above), so I'm thinking about getting the 5 ohm Dyna coil they have.
1981 KZ440 LTD

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