I have a Kawasaki Ninja, ZX6r, 1997 F3. The bike starts great and rev's great when standing. At high rev's its as sweet as a nut. The problem seems to be when riding the bike and the revs are below 4,000. When you twist the throttle, the sputtering is terrible and it struggles to pull - however if you go really gently with the throttle the bike will gradually work its way through the sputtering and once you break 4,000 rev's its away like lightning. it doesnt make a difference if hot or cold. I have new fuel in the tank, I have changed the plugs, changed the HT leads, changed air filter. Also had the bike looked at quickly by a Kawasaki employed mechanic who checked all the air inlets etc and said everything is as it should be. He also stated that because the bike rev's so well at higher end its doubtful its a carb problem. Anyone else out there had this problem and if so, how did you fix it?