Does your float rattle if you shake it? if it does that's usually a sure sign that it has a leak.
On the older carbs, there is often a small "O" ring in the part that the pin goes into. Over time, this can perish to a condition that won't stop the flow of petrol when the float rises.
Also, although your float may be okay in water, it might not be ok in petrol.
Your float doesn't exert a great deal of pressure on the needle when it's in the float chamber, so if it, or the needle seat, is in anyway faulty, it won't work properly
If yours is a machine that hasn't been used for sometime before you have started to work on it, it may be that there is some "muck" up the part where the float needle(pin) goes, that is stopping the pin from seating correctly. It won't have to be a very large bit of debris to keep the petrol flowing.
If you need to get parts, then Meetens may-well be able to help.