First, do as suggested and find out if the engine is rich in the needle-controlled region. This is about 1/4 to 3/4 slide opening. First do a full throttle plug chop to make sure your main jet is correct then do a plug chop at about 1/2 open (have a look, then mark the twist grip somehow at that point).
You don't have to completely disassemble the carbs. You have to remove the carb stack (2 & 3 are true buggers to get at otherwise) and take the top covers off the carbs. Bend back the lockwasher and undo the bolt holding the lift arm to the turning shaft. If you slide it over a bit and lift the slide, the ball on the lift arm will slip out of the link arm, you have to press in against the spring a bit. Then lift out the slide and needle, remove the 2 phillips screws, then you have to rotate the screw plate to line up its tang with the carb slide slot and it comes out. Remove the needle, press it down on a hard surface with the clip open side down (and with a finger on the clip or it will spring up and away) and the clip will snap off. Put it in the groove you want and snap it back on the same way. Do not lose the clip!!!!!! Now reassemble the slide/clip/link arm.
The fiddliest bit is getting the link arm back on the lift arm, there's a tiny graphite (?) button that has to sit on top of the ball and be the right way up. You can get the ball to go in by fiddling and pushing the lower graphite thingy down with some small tool, this is quick once you get the hang of it. If you just can't get it in, flatten the other lockwasher and remove the cap nut on the link arm, and assemble it that way. Just don't lose that graphite button - it goes in pointy end up.
Once reconnected and sealed up, the carb sync will be slightly messed up but not enough to worry about while doing carb tuning. Once you're happy with the way the plugs look through the throttle range you should resyc the carbs
