TOPIC:

Looking for advice.

Rebuilt the 81 KZ650 and did the AFR with the colortune so they're each just yellow. idles beautifully. One thing I noticed after a few minutes of idling, cylinders 1 & 2 run hotter than 3 & 4. There is a noticeable difference to the touch on the cam covers left and right sides. It is a real problem because the jugs are painted and the left side is becoming discoloured. I assume it is both 1 & 2 but it may be only one of them.

Not sure how to troubleshoot this issue. I will check the AFR again and look at the carb sync in case there is a difference causing 1, 2 or both to overheat.

Any thoughts would be appreciated.

Jim

A simple and painless way to determine if there is a dramatic temperature difference between cylinders is to load a plastic spray bottle with some good, old fashioned water, and spray a litte on each exhaust pipe near the head while the engine is running. Notice how violent the sizzling is and how quickly the water evaporates. It will be more violent and quicker on the hotter pipes. If you want a more accurate assessment, a decent infrared thermometer will do the trick.
A more painful and expensive way would be to grab each pipe and pay attention to how much flesh is charred and how quickly. This is not generally the recommended method.

TexasKZ wrote: A more painful and expensive way would be to grab each pipe and pay attention to how much flesh is charred and how quickly. This is not generally the recommended method.

Nonsense! Just lick a finger and touch the pipe real quick!
But seriously, whether you do that or the spray bottle, the water (and/or saliva) should sizzle pretty violently and evaporate off the pipes darn near instantly. What leads you to the determination that 1&2 are running hotter than they should? Just the paint discoloration?

If you have the stock ignition coils & spark plug wires, I would redo the plug wire connections at all points. the plug wires unscrew from the coils by unscrewing the ribbed compression boots. If there's oxidation on the plug wires, nip off the ends. or go ahead & get new. I solved an intermittent firing problem by redoing the connections, then later got a new Dyna spark plug wire set when replacing the ign coils.

Coils. Check the coils to see if they're getting hot. press hard with your fingers. they should be warm, not hot. Mine were very hot, so I got new green Dyna 3.0 ohm coils from Z1Enterprises.com. the grey Dynas are a closer match for the stock electronic ignition, but I got the green ones in case I had to get the Dyna S. I replaced the spark plug wires at the same time.

Battery. make sure the battery is good & fully charged and do a load test. the motorcycle needs a good, fully charged battery to run right. I use a Ctek US 0.8 smart charger & VC97 digital multimeter. I have the same motorcycle.



...

A few drops of beer, then dispose of the rest as you see fit.

I would check the vacuum level of the carbs to ensue they are all the same. Also, how long are you letting the bike sit there and idle, and what is the outside air temperature? If the air temperature is pretty high the air cooled engine can get pretty hot rather quickly if the bike is stationary. Ed

Warren3200gt wrote: A few drops of beer, then dispose of the rest as you see fit.

That is alcohol abuse!

TexasKZ wrote:

Warren3200gt wrote: A few drops of beer, then dispose of the rest as you see fit.

That is alcohol abuse!

Your concentrating on the wrong part of my post. Any excuse to open a tinny will do for me !

Yes. not sure if both 1, 2 or both are the issue. The discoloration was quite evident after a short idle period. Mind you since then, I have found that 4 is not firing due to a faulty new spark plug. Replaced it ok but not run the bike yet so it may just be that which was causing the difference on each side. The discoloration may also now occur on the side of 3 & 4 now which I suspect may be due to a clear-coat that was applied over the paint. Don't ask who put it on as it will cause me to lie...........
I intend to get the jugs and head aqua blasted when I remove them to replace the piston rings due to low compression I recently checked. I will get back onto it on the weekend and let you know the outcome.

Jim

Just in case something isn't connected correctly. the cylinders, spark plugs, etc are numbered 1-2-3-4 .Left-to-Right .sitting on the motorcycle.

RH ignition coil = 1-4 spark plug wires with red (+) & black (-) primary wires.

LH ignition coil = 2-3 spark plug wires with red (+) & green (-) primary wires.

The stock coils are embossed with (+) & (-) at the end near the primary terminals, but I'm not sure if it matters.
I would go ahead and connect red to pos (+) & black/green to neg (-). see the 1981 KZ650 service manual. section 6-6. Polarity of ignition coil.

There are resistance checks for the ignition coils in the manual. The coils can test good but still be bad, especially when tested cold. Inspect them for cracks or damage. A simple check mentioned previously is to ride the motorcycle to fully warm it up, then feel the coils to see if they're getting hot. press hard with your fingers. they should be warm, not hot.

Was it a resistor plug? I've seen those fail more often than non-resistor. I don't even see how a non-resistor plug can fail, but it probably happens.