The newest OS AX series engines have the HS needle adjustment right on the carb, but the engines come with a needle valve adjuster extender. It's a piece of thick cable (thick meaning 1/32" or so) that fits exactly right in the hole in the needle valve and is secured with a set screw. The needle valve is angled to the rear of the engine so that with the extender, it is easy to get to and keeps your fingers out of harm's way.

The length can be adjusted to your comfort level then the knob is secured to the end of that cable. See picture.

CGr.