Sometimes theres no spark

Alright, I know some of you are so bright and helpful, so why not give this one a try...
I've had this issue for a couple years now, and I guess that its just not going to go away on its own.

The Bike:
1979 KZ1000ST (shaftie) 20K original miles

The Location:
Fresno, CA

The Problem:
Sometimes 2 cylinders stop firing (the 2 on the left if you sit in it).

When:
It happens when I ride it till its warm, then park it for a bit, then fire it up again, but not always.
It happens more often when its parked in direct sunlight, but not always.
It happens more often in the summer.
It NEVER, EVER happens when I first fire it up for the day.
Sometimes when I'm nursing it back home, the 2 cylinders will spark back up, but not always.

What I've done:
I've replaced the coil and the problem persists.
I've checked and double checked all the wires, and everything seems to be in order.

What I think it is NOT:
I don't think its a air or gas issue, because there is flat out NO SPARK.
I don't think it is a loose connection, because it would be affected by movement or "jiggling".
I don't think its caused by a low battery, because I've replaced it.
I don't think its the coil, because I've replaced it.

What I think it is:
I think that the heat from warming up or direct sunlight is causing something to expand and then cut off the electricity to the coil.

What I want to know:
WHAT YOU THINK IT IS!!!!

lets see do you know if you have points or electronic ignition, if you have points then your gap could be incorrect too small and the gap will close causing no spark to large same problem

also if the points weld them selfs together you'll have the same problem

Post edited by: jbw7300, at: 2006/04/20 20:05

jbw7300 wrote:

lets see do you know if you have points or electronic ignition, if you have points then your gap could be incorrect too small and the gap will close causing no spark to large same problem

also if the points weld them selfs together you'll have the same problem<br><br>Post edited by: jbw7300, at: 2006/04/20 20:05

Except that he says it's the left two cylinders, and that would be #1 and #2, and each of those cylinders is on a separate coil. AFAIK, #1 and #4 are on one coil, and #2 and #3 are on the other coil, so that pretty well eliminates ignition issues.

Have you checked the valve clearance? And do a compression check when the motor is hot. I think you probably have a heat related mechanical issue.

Thank you for your replys.

I believe that I have electronic ignition, not points.

I checked valve clearence 1 year ago.
Very minor adjustment performed.

I've never checked the compression, but the bike hauls ba**s. How would low compression cause my symptoms??

I agree with you that the problem is most likely heat related.

I'll check the compression soon and post the results.

I've never checked the compression, but the bike hauls ba**s. How would low compression cause my symptoms??

If there was not enough valve clearance, then there would be a possibility of the valves expanding when hot and not closing all the way, thus a decrease in compression. But you say the valve clearance has been checked less than a year ago, so we will rule that out for now.

You say there is flat out no spark, and that point I can't understand because they are on two different coils, if those two have no spark then the other two should not have any spark either. The elctrical circuit goes from the coil, through one plug wire, jumps the plug gap, through the head to the other plug, jumps the gap, then back to the coil, like a circle, break any part of that circle and neither plug will fire.
I just thought of one way you could have spark at one plug but not the other. If one spark plug wire is shorted to ground then the other plug will still fire. In your case both left side wires would have to be shorted to ground. You don't have them pinched against the frame somewhere do you?

You have me puzzled so now I am going to drive you crazy with questions until I find out why this is happening :evil:

Post edited by: steell, at: 2006/04/21 02:31

The 2 cylinders that stop firing are the 2 on the left if you sit on the bike.

These 2 are connected to the same coil on my bike.

Thanks for the deep thought, but don't blow a fuse.:S

LET ME CORRECT MYSELF!!!

The 2 cylinders that have the issue are 1 and 4. NOT 1 and 2.

Sorry for the confusion. I owe you a fuse.

del

I'm glad you said it was the 1 &4 not the 1&2.

You may have a bad pulse coil on the ignition plate for the 1 & 4 coil. I'm sorry I don't know how to check it or fix it. Check the archives especially loudhvx posts

Post edited by: OKC_Kent, at: 2006/04/21 21:15

When the problem happens, check for spark to verify it is gone, then quickly swap the green wire and the black wire which go the the two coils. Now check for spark again. It should be gone from the 2 & 3 cylinders (that is if the coils are good).

Restore the wires the way they were. (Spark will be gone again on 1 & 4.)

Next is to swap pickup wires if you have electronic ignition. Swap the black and blue, and also swap the red and yellow. This is more difficult since the connector is hard to work with. You may want to make 4 little jumpers to accomplish this.

If the problem now moves to cylinders 2 & 3, the problem is the pickups. If the problem stays on 1 & 4, the problem is in the ignitor.

Of course, it can also be a bad wire heating up just enough to flex and short against some metal etc. blah blah blah. So while you're in there do a very close inpection. I assume you've tried wiggling wires while it's running?

camperstyle wrote:

LET ME CORRECT MYSELF!!!

The 2 cylinders that have the issue are 1 and 4. NOT 1 and 2.

Sorry for the confusion. I owe you a fuse.

You were just trying to drive me crazier

In case you are unaware, loudhvx is the resident electronic ignition expert, so follow his advice