Motorcycle Repair: gpz400 poor running, gpz 400, shively

Question
bike is sluggish up to 3000 revs then ok to 5500 then hits a big flat spot till 7500 then pulls like a train. bike wont rev over 6000 in 6th gear. had new cdi, fuel filter, carbs cleaned ,plugs changed, air filter ,running out of patience now which is a shame cos bike is in good condition otherwise. its a 1985 gpz 400 zx  

Answer
Hi Sam,

With the limited information given, I suspect the carburetors need tuning to correct air/fuel mixtures. I also suspect an intake air restriction.

Did you perform the above mentioned work? Were the carbs badly varnished? Describe the appearance of the spark plugs.

Respectfully,
Mark Shively