rman

Hello to all I'm a newbie and need your help. Just bought a kawasaki 2004 ultra 130 that was used in greenwood lake nj only. On the test drive it drove off idle to max great. tralered it to my lake and when my wife got on at the dock we rolled twice but not while it was running. No water in the engine area. Now off idle to about 22 MPH there is a hesitation all the time. I've change the spark plugs and added stp fuel injector cleaner to the gas no change. the dealer said that stabil was used during winter prep. Low hours and when you hit the throttle it goes like hell. Any suggestions such as draning the gas with ne? Cleaning the screens above the throttles?
Thanks
Rman