[old ugly]

Lightman7

a few things i have found.

you say you had the needle out and there were no bits inside. the other thing i would do is,
-with a q-tip and a bit of rubbing compound twist the q-tip on the brass where the needle seats, just to clean it up. (i know it is new but i do that to the new ones.)
-on the top of the float where the needle rests you may see a tiny divot from years of the float going up and down. with very fine small pc of sand paper level that dimple off then polish that spot with rubbing compound. (i don't know but maybe toothpaste will work) if the new float doesnt go up straight into the seat it may leak..
-if in the past someone has bent the float to try to set the fuel level that may be an issue, not pushing the float needle up straight into the seat. in which case you would have to buy a new float.
-those new washer for the valve that you use to set the float height should be good. maybe the casting where they contact the carb may be ruff. you may be able to tighten a bit more. i have snugged that valve quite tight with some success. just don't break it.
-i have had floats with tiny leaks that will slowly sink. if that is the case you should be able to hear gas inside it. (likly not your problem.

do not put any sealer on those gaskets. it will cause you greif if it gets into the jets.