You have two needle valves, one on top (low speed) and one on the bottom(high speed).
Static settings:
Low speed = 1 1/2 turns out from lightly seated.
High speed = 3/4 tuen out from lightly seated.
Final adjustment should be made with the boat in the water.
Maybe. It looks like it's sticking somehow. But it may be possible that it's fuel soaked.Sounds like it needs to be cleaned and inspected, float is probably shot.
Yes, 4423 is a 3.3 horsepower 1947-51 Sportwin.
If the float is shot, you can modify a Mercury float to work. Part number 18-7208, here at iboats.
The float valve has no separate seat. If the seat is bad, you have a problem.
I guess I don't have to tell you what a monster that carburetor is. Good Luck. You are going to need it.