Tank, Airbox, etc off. When you look down on the carbs, spot the 4 jubilee clips that hold them to the inlet rubbers. Loosen off the screws on them, when the clips can move freely stop loosening. The bank of carbs will then pull off (may need some gentle wiggling as you pull). If there are restrictor washers they will be sitting between the carbs and inlets rubbers so once the carbs are off it'll become apparent.
Reassembly is the reverse of the above, if the rubbers are old and stiff it may require a bit of wiggling to seat the carbs properly.
There are other ways to restrict a bike, throttle stop would be the obvious one, that should be easy to visually check for.
Is it definitely topping out at a ton? The bandit will do 120-something but that last 15-20mph will require a fair bit of road to get up too (and probably require you to be flat on the tank).
Other thing..... is it running standard sprocket sizes? Previous owner may have altered the sizes to gain acceleration at the expense of top end.
