I have a 1995 zx-9 that I bought new back in 95 it has had a flat spot at around 4000 rpm since I have owned it. I have had it looked at by a couple different machanics and they have tried adjusting it with some success. I had to have the some parts in the carbs replaced and know the problem is worse. I ahve noticed that if I leave the choke on a little it fixes the problem so I am assuming the carb is running lean. I have talked to a couple of bikers that had this same problem with this model. hoping to get some direction to try and save some money with the tuning process.any thoughts?

Looks like a d & d pipe on it ,, is it a full system or just a slip on ? if a full system you'll need a jet kit and a timming advancer would'nt hurt either ,,, but if it's had the problem since day one ,,, you should've taken it back to the dealer a.s.a.p. and let them deal with it before your manufacturer waranty was expired, a dirty air filter, valve adjustment are also possible cures in addition to the jet kit. float highth in the carbs , jet size and needle highth will all change and improve your over all peformance...if it's done had all that ,, it was installed wrong ,, get it on a dyno to tune it correctly with the air/ fuel ratio at 12.5 - 13.5....good luck.