09 TM EN 300,after the bike is warm and ridden for around an hour or so,it splutters and misses under quarter throttle intermittantly..Clean carby jetted well..Electrical issue im thinking?Anyone help..Cheers

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Not 100% on the KPS but my guess would be a 20 year old bike I doubt if a after market cylinder would be available so more than likely still the original? The stamp KPS may even be Kawasaki Production System logo but again not 100 % Low compression would be a likely contributor to spits and splutters at high revs - some other likely possibilities would be spark plug breaking down at high load, fuel mix bit high in oil, partial blockage in carbi jets may be limiting fuel when wide open throttle.Any of these could give coughs and splutters at high RPM's These days you generally only resleeve the cylinders rather than rebore but if your cylinder is in not to bad a shape then a simple honing tool can clean them up quite nicely If you about to rebuild with new piston kit and gasket kit I would recommend full compressed air clean of the carbi as is all off anyway would only add hour or so to do then with your new piston kit you would be back to full power again
I not certain with Kawasaki ratings but all the Yamaha YZ's I build and race the pistons are only rated for 20 hours use your's would not be to much different I would guess
Good luck with your rebuild from the sound of things you should be back to normal as soon as you button her back up
regards Jamie

Try changing the spark plug first and clean the air filter.

first drain the carby, then set your air mixture screw 2 turns out, from the fully turned in position. The starting proceedure is as follows, when the engine is COLD, turn on fuel, pull on the choke fully, and kick the engine over. DO NOT use any throttle, when the engine is cold, and the choke is on. Remember Choke on, NO throttle.
When warm, no choke, and a little throttle when kicking.

you need to remove the carbs and they need to be cleaned, what has happened is the gas went bad and it has gummed up the throttle shaft and most likely lots of other parts in the carburators, these sound pretty bad, what needs to be done is they need to be completely disassembled and soaked in a strong solution to free and clean everything up, you are looking at about a $300-400 bill at a shop.

Check your carb systems and fuel delivery systems

Could be your cdi box or possibly coil. How strong is your spark?

Your bike may be jetted too lean. A common problem in these days of overzealous EPA regulations. You can tell if when you've cranked your throttle wide open and it splutters, if you back off on the throttle about 1/8 to 1/4 turn, it clears up. This is indicating that it is jetted too lean. When you close the throttle slightly, the fuel is being metered by the main jet and by backing off on the throttle a bit, you're cutting back on the air, thereby bringing the mixture closer to what the engine needs. Try rejetting the carb, Go up one or two sizes on the main jet, one step at the time.

Now, it could be too rich as well. If it splutters and blows black smoke out the exhaust, it either jetted too rich or the float level in the carb is set wrong.

Take care of the simple stuff first before rejetting the carb. Make sure your spark plugs are the correct ones and they are not fouled from overusage of the choke or enricher. If you allow the bike to "warm up" with the enricher on, plug fouling is common with this practice. I get the bike started and as soon as it will run without the enricher or choke on, I turn it off and keep the bike running with the throttle. Don't foul as many plugs that way.

Sounds like a carby jetting issue. Sounds like she's running lean above idle, after you zero the enrichener. Suggest adjusting the pilot air screw ( air mixture screw) under carby. You need to remove a blanking cap to do this. See eg Buzz Buzzelli's book for this, or a Sportster forum. I'd back it out to 3-3.5 turns, very gently by 1/4 turns till she runs well. Good Luck.

1. The carb could need cleaning.
2. Sounds like the exhaust pipe needs to be de-carbed.