You're right, changing the slide needles on these carbs is a serious pain. I've done it several times. You want to take off the bolt holding the slide linkage to the arm so that you can move the slide freely and independently of the others by wedging a small screwdriver or a hook/pick under the arm and lifting. That ball joint is held in place by a spring pushing up on a short concave rod on the underside of the ball joint, and another concave rod pushing down from the top. It's hard to describe but you'll see once you have it apart. Undo the tabbed washer and take off the top nut holding down the rod and don't loose either. Now lift the arm up with a tool so you can grab hold of the arm between your thumb and forefinger with one hand, and with the other hand grab the part of the slide that links up with the arm. Now apply pressure up and down so that you feel the play in the spring, and when the spring is fully compressed pry the ball joint of the arm out of the slide linkage. Reverse order going back together. It's really hard to describe but once you do it a few times it gets easier.
Once you get the slide out you have two tiny screws holding a stay plate down inside the slide. BE CAREFUL not to strip these! Find a screwdriver that fits the heads perfectly. They are a PIA to drill if you have to!!! If the heads are damaged, do yourself a favor now and replace them with small Allen head screws. Also, change the needles one at a time, or try not to get them mixed up, as the linkages and slide cutaways are oriented in a specific direction.
Sorry if this doesn't make sense, it's the best I could describe the way I do it... And yes, I am incredulous that this task is so complicated!
