I have a friend who fought some ghost of a problem a lot like this for a long time. Rebuilt carbs, frequent plugs, new coil, I think a new stator... can't remember for sure on that one. Anyway, the final change that made it all go back to normal was swapping the CDI out.
I also had strange problems from my CDI. I had a MSD that was used. I had strange behavior on my ski too. I put the stock ignition back in and the problem was resolved. CDi can make very weird things happen.
Yesterday it happened (i think by coincedence) at the moment i changed from on to reserve.
You can't just change from on to reserve and keep going nuts. The reserve line is often dry or has air in it. When switching from on to reserve, you need to stay in the lower RPM until the fuel line is fully primed and air free. When you start your day, before you ride at all, warm the ski up on reserve, then switch to on and stay lower in the RPM until you know your On line is fully primed, then enjoy. You should never be on the track racing or taking a high speed cruise and swap over to reserve at high RPM. If you have a good reason to do this, start the day as I said before, or you risk a lean seizure as high RPM with dry fuel lines and risky business.
Didnt cleaned the carb myself, but im thinking of doing it myself again because it didnt get taken apart, just thrown into the ultrasound cleaner...
Whoever did that job didn't do it right. That wont get a internal fuel filter clean. A friend had a GP800 that was 80% clogged in one and 100% clogged in the other. That requires disassbly.
Get a popoff tester. Take the jet side apart and the fuel pump side apart. Clean both with carb cleaner. Don't forget the little fuel basket on the pump side. Re-assemble and use a pop-off tester to both check that your needle is working right (Pop-off test - affects mostly low end performance) and your fuel pump isn't leaking (pressure test - mostly high end performance).
PS: I'm not suggesting this is a carb problem. Sitting rarely fixes carb problems.
Before running i opened up the front high speed jet 1/4 more, because if was suspecting that this cilinder was running lean.
Lovely evening with running the jetski hard, then at some point, completely died. Wouldnt start again in the water. Would start on the shore (no load), and thus had spark.
Checked compression later in the evening and still same results. Also checked inside the engine with the camera and i noticed something strange. The last time i checked, both pistons where almost completely black with chips missing around the ports, but now the rear cilinder was almost clean, with some kind of black spots at the center of the piston. Front piston was still black.
I will try to take a picture.
Don't suspect the cylinder is running lean. Know it is or don't mess with it. The most common way to know this is by doing plug checks. There are lots of posts here on the X about the right way to test this. You can also be sure by checking piston wash, something I haven't ever messed with, but piston wash is what you are alluding too with the differences in the carbon build up on your two pistons. Look up and read some threads using the key words plug tests and piston wash. I have found it easiest to search using googing and x-h2o.com "piston wash" rather than the forums search feature, but these days the search is working a lot better than it used to.
It's unlikely you are having seizures. You'd see scoring on the cylinder walls and lost compression or heat damage on the exhaust side of the piston. Not to say it's impossible, but it is unlikely.
At the end of the day the jetski suddenly dies, like the stop button is pressed. It wont start after, but will once in a while fire, so this can sort of rule out ignition problems (it will crank, but not start)
After an hour everything is fine again.
No, you can not rule out an ignition problem like this. Not at all. The starter and the ignition are two separate systems that work together but are not dependent on each other. One working does not prove the other works. Yes they are connected, such as you can't crank the starter without the lanyard on because of how a yamaha is wired, but that's not how a kawasaki works. A kawasaki does not separate the lanyard, so a kawi will kill the spark and let you crank it, which is exactly the symptom you are describing. You can't make this mistake on a yamaha because of how the lanyard is wired, but the cranking does not mean you have spark.
You need to test that you have spark. The proper and safe way to do this is to use an in-line spark tester tool. You don't need one as most of us simply arc the spark plug off the cylinder head bolt to make sure we have spark. I can't say I recommend this because because if you have any sort of fuel or exhaust leak and start sparking off outside the motor you can cause a combustion (long story, but I once caused an explosion doing something similar), but yes, I myself do this, and no, I don't have the inline tool.
You can't rule out your ignition as the problem until you have confirmed you do have spark. It sounds like you haven't. Stator, coil and CDI failures often start as intermittent electrical problems that come and go often related to heat. As BK said, heat in the coil and heat in the cylinder are not related.
BTW, having spark does not rule out a CDI/Coil/stator problem. My MSD failure occurred at higher RPM. I didn't have starting issues. However since yours is not starting you can definitely check spark to know if you have an electrical problem (just know it doesn't completely rule out one). Unfortunately they only way to test a stator/coil/cdi is often to swap them out and test again.
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Im rebuilding the carbs right now.
Assembling then now. Look at the space between the needle and the thingy that lifts the needle up. Is that ok?
It's very unlikely your problem and yes it looks fine. Only replace carb parts with genuine mikuni parts, (almost) never should you bend that arm as it has to work with the diaphragm, there are some good videos on youtube about it. Familiarize yourself with popoff testing and leak testing. Both are applicable to any ski you will own, regardless of how it is tuned, because those two tests are simply to ensure the carb parts are functioning correctly before you waste time trying to tune out a leak.
Note that the color of the rear cylinderis very different then the front cilinder. At this point i dont know which color it should be anymore. Also the chips at the ports in cylinder 1 are color brown. Piston number 1 is almost completely black.
