What year? I think the older ones had a different needle.

I suspect the lack of clip positions on the later needles is an attempt to satisfy an EPA requirement that the carb not be easy to adjust....same as the brass plug over the idle mixture screw.

Whatever method is used to adjust the height of the needle in relation to the slide (moving a clip or changing the spacer height), will make a change in the fuel/air mixture.  When you raise the needle in the slide (lower clip or trim white spacer or reduce the number of washers), you will make the fuel/air mixture richer.

If the needle position causes the mixture to be too lean, the engine tends to have a flat spot, bog, low power or surging at throttle settings a bit over 1/8th throttle.  If you move the throttle so that you are accelerating like normal traffic on the way to church.....and the bike is surging - but it runs smooth at full throttle - you most likely need to raise the needle to richen up the mixture.  When the needle is too rich the bike tends to blubber and make strange noises when you roll off the throttle, and it gets poor fuel mileage.