Jet ski carb problems?

[John W]

I recently bought a Kawasaki 750sx and it has a Keihin CDK II carb. The engine idles great and fires up first time. It also launches out of the hole with 1/3 to 1/2 throttle but once I break about half throttle it will quickly bog down and usually die. 5 seconds later it will fire back up and do the same thing. I can certainly give it full throttle in very short bursts but 2-3 times of that and it dies as well.
I'm assuming this may have something to do with the main jet screw but I'm not sure what is happening. Do you think it's flooding or running so lean that it can't operate? If you have any input I'd appreciate it.