Spark Plug: Overheating on a Colder Plug?

Replaced plugs with Kawasaki-recommended B7ES; ran differently, but not good, and the problem still persists. However, I think I discovered the source of the balancing issues - low compression in one cylinder. It's causes the cylinder w/ high compression to run lean (makes sense I think).

Standard operating temp compression is 156 PSI. since I tested multiple times and got similar numbers, I'm pretty confident in the numbers below, except the "cold test w/ oil added" - I may have added too much oil. I know testing cold is not ideal, but it was more of a sanity check than anything.

Left Cylinder

Tested Cold - 140 PSI
Tested Cold (after adding oil) - 160 PSI (may have added too much oil?)
Warmed up - 140 PSI
Warmed up (after adding oil) - 150 PSI

Right Cylinder

Tested Cold - 90 PSI (may have had residual oil from previous test, causing a higher number?)
Tested Cold (after adding oil) - 110 PSI (may have added too much oil?)
Warmed up - 80 PSI
Warmed up (after adding oil) - 80 PSI

With what little difference there is between compression PSI "warmed up" and "warmed up w/ oil added", this is a pretty good indication that there isn't much blow-by at the piston rings, right? And that means it is either a valve not seating properly, or a head-gasket leak?

I've been told several times to do a leak down test, but I still don't see how that will help me diagnose the source of the low compression. Won't it just show that I am leaking air?

Also, not sure if this info would provide any insight, but after rebuilding the engine and running it, the compression in the right cylinder first checked out to be about 120 PSI - cold test. It has since dropped to about 70-90 PSI consistently.

Checked the valves? one or more may be too tight, as the engine heat causes the tolerance to shrink, possibly burning a valve. These engine run best with a little noise, it's when they get quiet, you should worry.

MFolks, Are you referring to the valve clearances? I have them all set at about .007"-.008". I guess I could check the right side ones again. I can certainly try setting them to .010"-.011" if more noise is the goal.

Glad to hear you are getting there, but it sounds like there is still a way to go, so, couple of things; you probably know most of this already.
The heat rating of the spark plug is referenced to the amount of heat it transfers to the cylinder head, for dissipation in the airflow, typically the spark plug is situated at the hottest point in the combustion chamber, the crown, therefore it is well suited to soaking up heat and transferring it into the cylinder head, through its contact with the head, down the threads and seat.
depending on the number, it will transfer more, or less heat away from the combustion chamber, a colder plug will transfer more heat away from the combustion chamber than a hot plug, which will retain more heat within itself before passing it on, this is necessary to keep the at optimal temperature and keep the plug clean.
The motor manufactures have spent many millions on R&D and come up with the best combination of specs, silly to try and change them, unless of course the motor is highly modified, but that is a whole other story, stick with what the book says.
The plugs are not cooking or fouling because their is a heat range issue, it is because of an underlying problem elsewhere, and this needs to be found.

it seems that your one cylinder is way down on compression, this issue needs to be addressed before anything else can happen, you can tune until the cows come home, the bike will never be right as long as that pot is not pulling its weight.
Sad, and I know that it is not what you want to hear, but that is the honest and brutal truth, we are here to help each other, not blow sunshine, and anyone who tells you it is not a problem is doing you a dis-service.
All is not doom and gloom, it may be something small and not necessary a motor tear down, you may have a vale clearance issue, as MFolks pointed out, you may have a ring issue, or even a scarred liner from a small end circlip that has come adrift, who knows, either way, we need to find out.
This is where a leak down test comes into its own, by pressurising the cylinder, you can hear exactly where the air is escaping, if you have a valve issue, you will hear it escaping out of the exhaust or intake port, if you have a ring issue, you will hear it escaping into the crankcase, remove the oil filler cap and you will hear it there, clearly.
If your plugs have been overheating for some time, it is more than likely a burnt valve.

Once the compression issue has been rectified, then we can continue to find the root problem, which may be electrical, or carburettor, or a mix of both.
The poor carbs normally take the rap for poor running a lot more than they should, 30 year old wiring causes more issues than carbs ever will.
I have seen guys tweaking and tuning for days on end and get nowhere fast, curse and throw their toys out the cot, because "these bloody carbs", a quick test with the multimeter shows they only getting 9v to the coils, and they can't figure out why the bike runs like cr#p????? :whistle:

First stop, before you do anything else...........(after you have sorted out the compression) is to check that you are getting a full 12V to your ignition coils, if you are not, you will have a weak spark that is not going to burn the intake charge completely and plugs that will be prone to fouling.
If you are getting anything below 12V to the coils, investigate and find out why, old wiring harnesses build up resistance, clean all the terminals, better yet, replace them with modern spade type terminals.
If you still can't get 12V to the coils, I suggest a coil relay mod, that will get the juice flowing. :woohoo:

As mentioned before, resistors, the bane of everyone’s life, use NGK - R plugs without the resistor, replace your plug caps, they too build up lots of resistance over time, leading to weak spark and plug fouling, and a cr#ppy running bike.
The NGK caps can be opened, I open them, remove the resistor and replace it with a piece of copper rod.
Now your ignition should be good to go, and you should have a healthy strong blue spark at the plug.

Only then can we turn our attention to the carbs to dial in the last piece of the puzzle.
The only way to get the carbs onto the sweet spot and dialled in perfectly is by doing plug chops.
Plug chops will show you exactly what your motor is doing and how it is running under actual real life conditions, which is what you want.
Do the plug chops properly and get the carbs dialled riht into the sweet spot, and I promise you, you will not recognise your bike, it will be smooth, have power and bags of torque you never even knew where there.
But it all has to be done properly, each system has to work in harmony with the other systems, there is no other way.
I do not know how familiar you are with doing plug chops, but if you want some help, give me a shout when you are ready and I will walk you through it step by step.

I hope this helped a bit.

440's had a little section on the rear of the air box that was sealed with a felt like material. As I recall it holds the air filter itself. The seal would go bad and they would run very lean. They were cold blooded back in the 80's. With today's fuel and that seal leaking, I could see one doing exactly what yours is. Back then, white ceramic insulators were the norm.

If there's no signs of boiling on the insulator [magnifying glass], you're not in an overheat condition.

If yours still has the complete air box, check that seal.

I should probably mention - I have pod filters on the bike that I added myself, everything else is stock. I have been told by a reliable source that I shouldn't have to re-jet the carbs even with the pod filters pulling more air. Would you guys agree with that?

Flyboy - thanks for the feedback. Agreed, I have determined that I need to get to the bottom of the compression problems, and that the plugs burning out are just symptomatic of a deeper issue. I've converted back to the original spark plugs so that's one variable eliminated. I am quite confident that my problems are not due to the carburetor, they're clean as a whistle and the diaphragms are in good shape.

I've seen the term thrown around - but what is meant by a "burnt valve"?

Where do I check to see if I'm getting 12v to the coil - between the pickup coil and the transistor igniter, or between the transistor igniter and the main coil?

Austin440 wrote: I should probably mention - I have pod filters on the bike that I added myself, everything else is stock. I have been told by a reliable source that I shouldn't have to re-jet the carbs even with the pod filters pulling more air. Would you guys agree with that?

No; you need a more reliable source. If you put pods filters on your carbs and did not re-jet you will have problems - this is an undeniable fact even from the most enthusiastic pods supporters on this forum. You must compensate for the difference in air flow that pods provide compared to the stock air box. In addition, you have a serious challenge in tuning for the carbs on your bike because it uses CV carbs. You may want to read the following study done by professionals. It discusses using pods on bikes, and in particular, discusses pods on CV carbs. Pay particular attention to the last 3 paragraphs on the last page as it is very specific about CV carbs & pods. Ed

kzrider.com/forum/3-carburetor/585949-po...-a-free-lunch#585949

Hi Austin440, what happens is, the valve gets too hot and literally starts to burn away,like putting an oxyacetylene torch to metal, you van see it in this pic if you look at the exhaust valve on the lower left.


Exhaust valves are normally the first to burn, as they run the hottest, the reason for it is very often a valve that is set too tight with not enough valve clearance, in an effort to make the motor run quite, people set the valve clearances too tight, and the valve does not spend enough time on its seat.
Remember, your exhaust valve is subjected to the hot exhaust gas around it all the time, as well as the heat from combustion, consider that your exhaust gas temperature is around 1250 F, it is easy to see how hot the valve runs, in fact it glows cherry red during operation.
The only way for it to cool itself is to dissipate the heat into the cylinder head for the short period it is sitting on its seat, so by setting the valves too tight, you reduce its time on the seat, and it just gets hotter and hotter until it starts to burn away.
A noisy tappet is a happy tappet.
Lean mixtures and timing set too advanced will do it as well, as they push up the heat in the combustion chamber.
A lot of exhaust valves have hollow valve stems and are sodium filled to help lead the heat away from the valve head and keep it cool.
Intake valves are less prone to burning as they are cooled by the incoming intake charge.

The only place to check voltage at the coil, is at the coil itself, measure where the low tention wire from the igniter goes into the coil, or as close as possible, probably at the plug right there by the coil.
Red or red/orange, red/yellow wire I think??
red side of multimeter to wire, black side earthed to frame, crank engine over and note reading.

And like Ed said, you need a rejet with pods, no matter what they yell you, it may only be slight, but it has to be done, otherwise you will run lean.....read first paragraph. :blink:

You ideally want a fuel/air ratio of around 15:1, fifteen parts air to one part fuel.
So it would hold true then, that if you allowed extra air into the engine by fitting pods but no extra fuel by fitting larger jets, the RATIO would change to, perhaps 18:1, you are now getting eighteen parts of air, for the same one part of fuel, leading to a lean run.
Hope that makes sense.

Oh, the simple things! I read Patton's posting on another topic about holding the throttle wide open when doing compression testing. So I figured I would give it a go thinking it might make a small difference. The right cylinder jumped from 80 psi up to exactly 156 psi. The left cylinder went from 140 psi up to 150 psi. It seems there is no shortage of important tricks I need to learn.

The discrepancy between the two cylinders without the throttle held open might just mean the carb throttle plates were way out of alignment with each other.

I have an analog multimeter so when I set it to the 50v dc setting it shows about 9.5v, but when I set it to 10v dc the needle goes past 10v. So I'm probably getting about 12v to the coils, and I have tested the coils to make sure they are in the proper resistance range - they are about 10-12K ohms.

So I think the next step is to order new jets and play around with those. The bike gets very bogged down between idle and maybe 8-10 mph, but when the rpms get up above 5,000 it really starts to take off. I did some research on jets last fall before my "reliable source" told me I wouldn't need them (to his credit, I don't think he realize what kind of carbs I had at the time; he does a lot of work with Mikunis - which maybe aren't as finicky with the jets?). I'm thinking of bumping up the pilot jet 2 sizes and the needle and main jets up just 1 size. Does that sound like a reasonable place to start?

Austin, if your bike is ripping on top, there is no reason to adjust your main jet. It has been suggested that you do some plug chops to determine jetting values.
Contrary to popular belief, throttle position, not rpm, determine which carburetor circuit is in use. Make some marks on your throttle indicating 1/4, 1/2, 3/4 and wide open throttle. If your issue is between idle and 1/4 your problem is the pilot circuit. If your troubles are at 1/2 throttle your troubles can be found in your needle jet. Problems at 3/4 indicates jet needle or elevation of needle. WOT troubles is a main jet. Test and you will know for sure. Paul