Hello i am new here but i to get straight to the point.. i have a 2003 ninja 250 that has a very very noticible flat spot around 4-6k rpm that only "sometimes" (happens all the time when turning) if i slowly open the throttle it wont have a flat spot it will run perfect but if i slam it open it seems to rev fine then at the same exact throttle position everytime it seems to just go flat for a split second and sometimes even longer. i had a stage 3 jet kit installed with pods & two brothers exhaust but i recently switched back to the airbox and stock jets thinking the jet kit was the problem but it still does it no differently.. and the idle seems to want to dip down and sometimes even die on me when i am rolling to a stop.. so i was thinking that it is a vaccum leak somewhere but i am not sure at all. i tried lowering and raising the needle position with no changes in the flat spot. so if anyone has any tips on this i will really appreciate it..

Your first step is to check for vacuum leaks. If you don't find any then the next thing I would do is take the carbs apart and clean them. You can also try some SeaFoam in the gas tank to see if that cleans out the carbs.

im actually in the next few days taking the carb completely off and geting all new vaccum hoses and clamps and taking it completely apart and cleaning. so i hope this fixes it

well if anyones intrested i fixed it. and i think the main problem was my idle air mixture screws where missing there washers. I put them in and my bike nearly runs perfect now. so if anyone has a bad flat spot check the pilot screw things and see if there sealed that might be the problem

I don't care how the 250 is tuned it's the timing advance that causes the flat spot in my opinion, its fixed and at about the rpm's you describe. i noticed it stock and it's still there under certain conditions regardless of jetting , intake setup, or needle height, not to mention idle mixture