2002 Mercury 50 4 stroke carb float needles

Good day. I have a 2002 Merc 50 4 stroke that I've got the carbs off for cleaning. On the float needle, there is a plastic insert on the top of the needle. It seems to me that the plastic tip should slide in and out of the top of the needle. On mine, these tips seem to be seized. This restricts the movement of the floats making the fuel level in the bowls very low. The result is the engine bogging badly on acceleration. My question; should these plastic tips be free to slide in and out of the needle or do I have another problem that I'm not seeing? Any help would be appreciated.
Thanks
Rod.

Take a very good look at the operation of the float and float valve.-----I think you might have problems elsewhere.