If it's a Japanese import bike they have speed governors on them that correspond to about 200kph per federal motor vehicle law.
It's not a fuel cut off, it shuts off ignition to two of the cylinders.
It's very easy to bypass, there are an extra couple wires going to the speedo and it's just a switch that's activated by the sweep of the needle. Figure out if the switch is normally open or closed, then either cut or short the wires going to it.