Cylinders 1 and 4 have ignition intermittently.

78 kz650sr

My symptoms are the bike will run on 4 cylinders for a short or long period of time but eventually, boom, I'm running on two cylinders. As I sluggishly make my way home the other two cylinders pop on and off randomly.

This is the fourth time and second bike this has happened on. It's my curse. I've gone through two sets of coils on two separate bikes. So four sets altogether. Two stock pairs and two brand new Dyna 3 ohm pairs. None of which I've ever bench tested but when replaced did the trick for several months. Could it be something other than the coil itself? A short before the coil? Electrical is the bane of my existence. If cylinders two and three always work, that means the short would be RIGHT before the coil, no? I'm not blowing fuses. I have a dyna S. Could that be involved? The key here is that the cylinder failure only happens intermittently.

Thanks, Gentlemen.

alexnelson wrote: 78 kz650sr...run on 4 cylinders for a short or long period of time but eventually, boom, I'm running on two cylinders. As I sluggishly make my way home the other two cylinders pop on and off randomly...cylinder failure only happens intermittently....

Given observable fat blue spark on every plug, and valve clearances within specs, would also assure that the float bowl fuel levels are correct (by performing the clear tube test) and not too high which may result in an over-rich mixture leading to plug fouling.

There could be various other reasons that might cause an excessively rich fuel mixture.

Spark plug readings??

Good Fortune!

coils can work fine and then have issues after they heat up
just to be safe get tester and go completely through ur harness and check for continuity ,crimps, insulation faults and such in the wiring
it would be AMAZING , but not impossible if the 1 and 4 carbs were the issue , too much of a coincidence

Does your bike have points or electronic ignition? If the latter, it's probably an issue with the pickup coil for the 1+4 cylinders. If the former, it is likely that the condenser is breaking up. Both can be heat related as in working when cold and failing when hot.

To verify if it is indeed ignition related, bring a strobe light on your next ride. WHen the cylinders fall out, hook up the strobe. If it flashes, sparks are taking place. If not, you do not have spark. Removing the spark plugs and checking for a spark is not reliable because a weak spark may jump in free air but fail under compression. The strobe/timing light is the simplest way to determine if you do indeed have spark inside the engine or not.

Hi, I actually read your post before replying :laugh:
Yes! The Dyna 'S' might be the culprit.
They do fail and do exhibit the symptoms you are having.
I've had a couple that would break down intermitently, sometimes after only a few minutes and other times they would be ok for weeks before playing up again.
This did cause a lot of headscratching and un-nescessary plug changes, carb strips and coil swaps ect.
I eventually switched the pick-up and coil connections from 1/4 to 2/3 and vise/versa to isolate the problem.(It moved the ignition failure to the other pair of coils)
A good indicator of DYNA pick up troubles is signs of the white contact paste on the back of the pick-ups oozing out the sides due to the pick-up overheating.

My fix wasn't that elaborate. my right coil would be fine somedays all day then somedays for 10 minutes. bake ast for a month because I couldnrt afford new coils. while riding it to the shop where I work on it

it started acting up so I pulled off on an access road, pulled the tank and started jiggling wires while keeping it running and you know it right coil would come and go then after enough jiggling it wouldnt work at all.

the female end of bullet connecter seems to expand when the engine warms up and loses connection not everytime but enough to make me pull my hair out.

I had all the wiring loomed up and tied up for neetness cut the wireties took all the tension off, and crimped the connector a little plugged it back in and no problems since. (knock on wood) couple hundred miles and 139.00 still in my pocket.

Andrews coils with 8/79-1/80 production dates- so I could use a set but doesnt need them yet

If not already done, could also check for internal fraying of the 12 volt supply wire to each ignition coil. The wire covering may appear flawless. Manipulating the wire might influence conductivity.

Good Fortune!

I would replace the dyna with the points and condensers and see if the problem still happens. If so, it's not the Dyna; if not it probably is. Ed

Swapping coils is one way to see if it relates to the cylinders or the coils.

faffi wrote: Swapping coils is one way to see if it relates to the cylinders or the coils.

Good suggestion. If the problem follows one coil, then it is a coil problem.

If not, then it is the Dyna S ignition, or some issue with the 1 and 4 cylinders thenselves, or wiring. Most likely it's a Dyna S issue, in this case.

There is another swap you can do to determine if the problem is due to the Dyna S, or something mechanical with the cylinders (carbs etc.). But it can also just be wiring.
You can flip the ignition rotor 180 degrees, and swap the primary wires on the coils. If the problem moves to the other pair of cylinders, then it's the Dyna S or wiring. If not, then it's a carb or cylinder problem.

Hey guys. I've been pretty silent on this thread. Just taking it all in really.

I was able to narrow down a few things.

1st - I bench tested both dyna 3 ohm coils. The primary winding seemed OK at a steady 2.8 ohm on both. Not 3.3 but hey. The secondary winding was around 12.00 consistently. According to the multimeter my coils are fine.

2nd - I fired up the bike. Ran great for about 7 - 8 minutes and then, like clockwork, cylinder 1 and 4 go. At this point I took off the lead of plug #1 and put in another new spark plug to see if I was actually getting spark. No spark at all.

So it looks like I've ruled out the fuel system. I'm happy about that.

I have looked all over for shoddy connections but can't find any problems.

I think the things to look at now are the Dyna S and the mysterious relay the previous owner put in.

Any other thoughts?

loudhvx wrote: You can flip the ignition rotor 180 degrees, and swap the primary wires on the coils. If the problem moves to the other pair of cylinders, then it's the Dyna S or wiring. If not, then it's a carb or cylinder problem.

I think this is going to be my next test. I'll let you know how it goes. Do I have to swap the secondaries for this? I'm thinking no, right?