So, thanks for the replies. Buggy was never rolled and have the fuel tank vent upgrade, and how do you check your piston return spring?
I was hammering down a whooped out trial, dealer seems to think either too much oil was installed (which is not the case, level was in between the lines of the sight glass). Had another person tell me to change my oil viscosity to a 15w 40, as the 10w 30 is too thin at the temps these run at.
i will adamantly tell you do not follow that other persons advice... the engineers at Kawasaki spent untold hundreds if not thousands of hours testing this engine to it's extremes with that oil viscosity. considering that most newer engines run 0w-20, the advice to switch to a thicker oil is old school thinking that doesn't apply to todays engines. there's a reason that this 1000cc engine can make 120HP while my 1000cc riding mower struggles to put out 20hp. everything from the design and materials in the piston rings, internal engine components, etc. all are designed to work with a certain weight oil. the dealer may be correct as if the oil level was at the top or slightly over when the engine was cold, and then as everything expanded the oil level could have been too high. start up the engine cold, let it run about 10 seconds the shut it off. it should be in the middle of the sight glass cold
edit: just checked mine and that same vent tube is dry.... check your air filter. if it's plugged it could be causing crankcase vent issues pulling oil into the intake chamber.
i would still re-check the tank venting. it's a simple check, and if the tank venting is not working the way it should then you will get the exact conditions you describe. take it out and hammer down, confirm it still runs like crap, if you then unscrew the gas cap and take it out and hammer down and the engine runs way better, then i'd be looking at a tank vent problem. not to doubt anyone, but a recheck of how the new rollover vent valve got installed may be in order. if it's upside down it won't allow the tank to vent.
the only other thing i can suggest to check that doesn't require any special tools is to pull the muffler/catalytic converter and see how it runs. if the exhaust is plugged then the engine will not be able to breathe at high throttle openings.
from here on out every thing else i can suggest to check requires special tools to do so. fuel pressure, ignition computer data stream and such. if you find anything let us know what you find. it may help someone else in the future.
FWIW: i installed a Dynojet Power Vision 3 on my KRX.... being able to check/display the data stream in real time (and record if necessary) is a great diagnostic tool.