My bike is a 1978 CB550K with the PD type carbs. Might not work for all bikes, but it was easy enough for mine.
I had already removed the carbs to clean them and rejet. The problem with getting at the needle clip was that tiny snap ring holding the assembly in place. At the time I couldn"t figure out how to get the damn thing off. So I put the carbs back on the bike, it ran better, but was still lean at lower throttle.
The essential tool(s) I found, was at my mom's office. She's a DENTIST!
I started at carb 4 since it was the easiest to get to. Figured if I could handle 4 then I'd move on...
1. Remove the top cover of the carb (2 philips screws)
2. Unscrew the set screw holding the arm to the throttle arm.
3. I used a skinny allen wrench to hold the arm up, makes getting to the snap ring much easier:
4. Pop off that snap ring! the dental pick tools need to be used simultaneously. Unfortunately I couldn't take a picture and hold both, so I took a pic of how each was positioned. Once you have them in the groove, use equal pressure and shoot the ring off, right into the bottom of the assembly, which is conveniently shaped like a bucket. Let the plastic O-ring fall in there too. Both are simple to fetch out later with one of the dental picks.
5. Remove the spring between the two arms. (Dental picks make this easy too) Slide the arm to the side and disconnect the joint. Pull out the assembly.
6. Fetch the snap ring and the O-ring before you go sticking a screwdriver down into the bucket.
7. Unscrew the two philips bolts to get to the needle clip. I read some peoples DYIs saying they rounded the bolts down there. I didn't have this problem at all, but be careful and slide things over to get a straight angle:
8. You can now adjust the needle clip, and reassemble.
9. Repeat for the other three carbs.
The only tough part of reassembly was...you guessed it... the little snap ring. I was able to pop it back on by holding it tightly with some little needle nose pliers. If you drop it in the bucket, just fish it out with the dental pick.
Disclaimer: I got these picks from my mom's office for free. She said they throw them away after so many uses because they become worn out. Ask your local dentist and see if you can get some old ones for free! No guarantees though. Not all dentists are as rad as my mom.