Obviously, I have not seen the inside of this carb and no one else seems inclined to jump in and straighten me out.
The needle in most carbs has grooves near the top with a clip in one of them, the clip is then held in place by the spring. If you do not have this and the relationship between the float and the float needle is not adjustable I guess the only choice you have is a smaller main jet.
It bothers me a bit that you have to fix a problem which did not used to exist by changing a part which should never wear. I suppose, if the slide needle never comes all the way out of the needle jet, then it could have worn, or the needle jet could have worn from the needle rubbing on it.