If the high-speed needle is barely open when the engine's properly-tuned, it usually means that the needle seat has been damaged at some time in the past. The only solution is a new carburetor body. The needle seat can become damaged if the high-speed needle's been tightened and not just closed, or if vibration has allowed the needle to move around. If you remove the needle, you'll likely see a shiny ring around part of the pointy part of the needle. That shows that the needle has had actual contact with the needle seat.