Right the long and the short of it is, my wife has a H plate cbr400, it runs like and absolute dream. From tick over it pulls clean and smooth all the way to the redline, no flat spots, hesitation, simply its a Honda
On the other hand my bike, also a H plate cbr400. Tickover is smooth, as soon as you try to pull away its into a flat spot (looses power) then clears itself around 2-2.5k and wants to launch itself into orbit. Not fun, although after riding it for 10 days i did perfect the art of launching myself! Then it pulls fine upto 5k and flats til around 6k (still pulls, just not quite the same urgency ), and anything over that and its back to being a Honda! We've changed the carbs, I've not ridden it yet, but if you open the throttle its still not picking up smooth til around 2.5k. Any possible ideas, could it have been cam'd?

id say flat spots could be jetting? i could be wrong, but it could be jets or needles causing over fueling and 'bogging' it causing the flat spot.

Best advice is to bung Graeme France an email, he might be able to suggest what to check, he really knows his CBR's

Cheers guys will try GF. As we've changed complete carbs wouldnt have thought about it being jets. But who knows what you get when you buy off eBay!