ORIGINAL: billd76
There are two ''lock'' clips on the needle. The clips work well until you get about 2 turns out, then the detents on the clips start to become un-effective, the detents that set in the grooves do not run the entire length of the clip. Poor design in my opinion.
I suggest pulling the needle valve completely out, then:
1) Replacing the O-ring.
2) Bending the clips to the center in order to obtain more spring effect.
3) Placing one or two o-rings in the groove of the needle (see attached schematic), in order to get some friction on the clips when they slide over that point. A piece of fuel tube may work as well. Note that the exterior diameter of this insert should not be so big as to prevent the spring action of the clips while they are over the metal portion.
If the position of the needle is consistent, and the clips are frequently on the groove, I would go for a more radical solution: sliding the needle inside the knob enough as to locate the clips at the right spot after normal tuning. The knob holds the needled by interference only; hence, it can be made slide cold or hot, which is even easier (see attached schematic).