If the bike ran fine before you touched the carbs, then it would seem you did something that has caused a problem. You say you replaced thefloat needles?
Did you check the float height?
It's also possible that something is blocking a jet, or the diapham(s) are sticking. If it seems to stumble with the throttle cranked wide open, but then "catches up" and runs fine, it would seem to suggest it is not starving for fuel but getting to much in the mid range.
First try shooting some carb cleaner through all the orifices and running some SeaFoam through the carbs. pull the intake boots off the carbs to make sure the throttle valves are going up and down smoothing and at the same time (with the engine off of course)
One little spec of goo can screw up a carb, so if none of the above work, you might have to take them off again and re-clean them.
Check the diaphrams for tears or holes, shoot Gumout spray through every hole and before you bolt the carbs back on, make sure the float valve is working, by using a small funnel attached to the fuel line and pouring some gas, (or seafoam) into it and seeing if the valve closes and does not leak.
You should check the vacuum line to the right air box to make sure it is not bottomed out, many cut the end at 45 degrees so it can't.