The two methods that I found best are to take a flat bit, and small socket taped together so if dropped it stays together. I know you tried that, but the way I learned to do it is, basically trial, and error. Assuming that you have it pretty close now, you could do like I have did in the past, which is to wait till the motor is cool enough not to burn yourself, and give it about a quarter turn in a chosen direction, before even starting the bike,and ride the bike, and see if it's better, or worse. If better, then the next time you ride it give it another quarter turn i in the same direction . If worse go the other way a quarter turn past were you started. I remember using a finger of my left hand to push the bit in position, and turning a little with my right hand. It's awkward, but can be done. That being said, I later discovered that I had a tool that made it a breeze to adjust, aside from not being able to accurately count the turns. It was a small flat squeeze ratchet type thing. It doesn't have a square ratchet drive, but rather a hex shaped opening, and if I remember right you just turn it over to reverse it. I had it for years, and that's all I ever used it for. I'm sure you can still get them, but don't know what they cost . I bought mine, along with another small tool set at a flea market type sale that a local Church was having. Unless you really like that carb, it probably would make more sense to buy a Nibbi PE28FL, or a Nibbi PEZ, which is the same as the PE28FL, except it has a little smaller inlet on the breather side. I will try to find a similar tool , and post a link, or picture.
https://www.amazon.com/CRL-Piece-Squ...4aAhNaEALw_wcB
I am surprised that they are so expensive. I got mine, and another small set of tools for $5.00, if I remember right. I did see that eBay had several sets used for much lower, but honestly, unless I am missing something, I have never had any use for them, except for the time, or possibly two that I used it on the mixture screw