On the OS46AX, the low speed needle is hidden away and very hard to find. It also requires a very small screw driver to adjust it. The carburetor throttling is done with a barrel that your throttle pushrod moves. The barrel has an arm the pushrod connects to. If you look at that arm you will see a hole in the center of it's base, the part that rotates with the throttle barrel. Look closely and you will see a screw down inside that hole. O.S. calls the slowspeed needle, the Mixture Control Screw. All you can see in the hole is the head of that screw.

It takes a very small screwdriver to fit in that hole. You adjust the screw with the engine stopped. The process is also described in the OS users manual on page 23. Unfortunately, they don't provide a picture.