davidinwa at comcast.net
Sun Aug 24 17:28:41 PDT 2008
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
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
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
Can the coils produce this sort of behavior?
Can the ignitor produce this sort of behavior?
Thanks in advance. Sorry for the long post.
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