Staggering

[David Fallon]

Hi All

This has been an ongoing project for a year now; a a 1980 KZ750 E.  I'm 
blessed because it seems to present only one problem at  a time.  This 
is a runner; I've brought it to life and gotten about 700 miles on it 
so far.

About a month ago it developed a noticeable hesitation and stagger from 
missing during low rpm operation, always between 1500 and 2500 rpm no 
matter the gear or throttle opening.  It got worse when it and the 
weather got warm.  The missing seemed to be intermittent and not just 
one cylinder.  Past the 2000 rpm mark it came to life and was a happy 
bike; idling it ran smooth and was a happy bike.  I check the valve 
clearance; it was good.  I checked the seal of the rubber carb mounts 
to the head; they were leaking a little.  I removed and sealed the four 
carb mounts.  I redid the carb cleaning thinking that it might be one 
of the air jets, but all pieces were as they should be.  Now they are 
double clean with no change in the staggering.  Yesterday, while out 
for a ride, it went on to the continuous staggering with almost no 
power.  I was a block from the house and it pulled itself home.  I shut 
it off and checked the pipe temps.  The 1-4 pipes were not quite as hot 
as the 2-3 pipes.

I suspected ignition issues.  I put an external spark plug in the #4 
wire and grounded the plug to the head.  When I started it, the spark 
seemed weak and intermittent.  I got out the manual and my VOM.  The 
pick up coils check OK.  The primary and secondary on the coils checks 
OK.  The Ignitor Ohm checks produce not exact  matches to the manual;  
the 200-500 ohm points measure 1600 ohms.  The 200-600 point measures 
1000 ohms.  The 300-700 point measures 1000 ohms.   I checked voltages 
to the various connectors; the battery voltage is low at 11.3 to the 
Red wire coming from the on/off switch to the coils and Igniter.  I 
jumpered in  full battery voltage to that Red wire while the bike was 
running and it made no difference to the missing/staggering.  All other 
voltages are good per the manual.  I tried to isolate the "bad" 
cylinder by using an external spark plug in one wire at a time and 
connecting the external spark plug to the head or that cylinder's spark 
plug while the motor was running.  There was no clear answer, but the 
1-4 cylinders seemed to be the least effected by taking them out of the 
"running."

I did notice that the visible spark on the 2-3 cylinders was much 
longer and more blue.  I removed the coils from the bike and tested 
them with a good battery as the source.  Neither coil makes a very 
impressive spark by just making and breaking the current to the coils.

I'm starting to run out of good ways to isolate the problem.  I'm 
hoping that someone's experience will help get me moving in a good 
direction again.

Can the coils produce this sort of behavior?
Can the ignitor produce this sort of behavior?

Thanks in advance.  Sorry for the long post.

David Fallon
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