Hey Nairns,
the bike fires right up but lacked power when i gave it full throttle.
Top end seems to be fine.
What your describing (if there aren't any air leaks etc) sounds like you need fuel idle to 3/4 throttle.
Will the bike run with the choke on? (easy way to see if your lean.)
It may stumble at idle, but if it improves your midrange.. you need more fuel.
A few other things you might check, throttle is closing completely, airboot look ok? Throttle slide worn alowing air around the slide and I've also seen carb cap lose the rubber seal in the cap sucking air...
Good luck,
Tuck\o/