Remove bar end weight.
Take all slack out of throttle cable with small adjuster under brake lever.
Undo the 2 allen bolts that hold the top of the throttle cable run on and remove the top part of the casting.
Unhook the throttle cables and you can then slide the throttle tube off.
Now, depending on which cam you have for your G2, the 050 will fit straight into the housing with no problems, the 025 however will require you take a dremmel to the lower part of the throttle housing and remove the cable runner casting on the front cable. (it becomes obvious when you get inside and take a look)
Remove grip from old throttle tube and re-install on G2 tube.
Follow the above steps backwards. Pay attention to any drag in the throttle as this could either be from the cam dragging on the inside of the housing or the rubber grip dragging on the bar end weight.
I find a small amount of oil on the inside of the G2 throttle tube aids with lube.
Dont forget to re-adjust your throttle cables