NEED HELP BADLY guys,

Our kawasaki ultra's (250 300 310) here in the philippines have a very common problem. they have low power problems some around 3000 rpm others like mine on 7000 rpm and goes back to 5500 rpm. we all have similar problems. we cannot find the source of this problem. what we did, we changed oil. we changed sparkplugs, we swap ignition coils from a brand new ultra same model, we also check our intercoolers for holes and water. checked the injectors, we checked our fuel tanks drained them and refuel. we run on salt water and we flush it properly. open seats when not used and always fill up full our fuel tanks to protect it from moist. but still the same problem occurs. please HELP. thank you what do we need to buy? or change or do?