Kinda hard to describe fully but I'll try... I am not about to do it just to illustrate the job.
The needle itself is easy to see but is difficult to get to. You really need the carb stack out of the bike.
Take the little top covers off each carb (two screws each). Be careful if they haven't been disassembled in a few decades, the gaskets are available but not cheap.
Under the cover is the link arm that lifts the slide. You will see a small hex head bolt at the shaft end with a bent D washer locking it in place. Bend the washer flat and remove the bolt: now you can swing the arm way up, then pull the ball joint apart sideways. You don't have to remove the cap and take apart the ball socket, and doing that risks losing the tiny bits inside.
Swing the arm back out of the way and you can remove the slide and its arm.
Now remove the arm by undoing the two tiny philips screws down inside the top well of the slide. Once the screws are out you have to rotate the arm to align its little tab with the slot in the slide.
Now you can finally get the needle out.
Be super careful taking the clip off and putting it back on. The clips just love to shoot off during either job, and are pretty impossible to find on the floor - or replace.
Reassembly is the reverse. Take a good look before reattaching the arm to the slide, the ball has to point towards the socket with the slide pointing the right way so its slot is toward the key in the body. Getting the ball back in the arm is not too bad - basically you wiggle the ball back in, opening the socket space a bit with a small tool may be required. Taking the socket apart takes much longer and risks losing the inner tiny pieces. Remember to bend the D washer back up to lock the bolt.
If you do more than one carb at a time, be aware that the slides can be mixed up: the aligning slots (slide to body) have two orientations and you can mix up the slides so that two or all four are in backwards (180 degrees out). The slide cutaways must all be on the air filter side of the carb throats. This sounds ridiculous but it happens - and if you only find it out when the engine runs like crap, there's no shortcut to correcting it... start again.
The joint between the lift arms and the shafts will not go back exactly where it was, so a carb sync is necessary after this job. That can be delayed until you are confident the clip setting is correct - the imbalance won't affect plug chops or EGA dyno tests. This just affects idle smoothness, making ignition timing difficult and final airscrew adjustment impossible.
