Gas is leaking out of the main throttle shaft, or gas is coming out of the top vents, or you get black smoke while idling. All of these are indications of too much gas, or flooding.
Here is a list of possible causes in no order of importance.
Most float valves (needle)
have a black Viton rubber tip on the end. The Viton tip needle may have been damaged when installing. Be sure not to put pressure on the needle when adjusting the float. A damaged Viton tip will allow too much fuel to enter the float bowl. Sometimes wiping off the Viton with mineral spirits to take any residue off will help.
Did you forget the gasket that goes behind the seat. Also make sure the old gasket was completely removed. See #22 in the illustration.
Check for cracks around the seat area. This would allow the fuel to bypass the needle & seat, so the fuel would never get shut off.
may be leaking causing it to sink. Heat up some water just prior to boiling and immerse the float. There should be no bubbles.
Gently move the float up and down. You should not feel any resistance or catching. A worn float pin, or improper installation of the float might cause this. If there is a metal clip that attaches the float to the needle, be sure it pulls the needle straight out. Move the clip around until it does. The float could be pulling the needle at an angle and it might cause it not to seal.
Check the venturi gaskets to make sure they are sitting flat and there there is no old gasket residue left under the new gaskets. See number 32 in the illustration.
Ethanol will leave residue behind and the small orifices of the venturi are subject to clogging. Use thin wire to clean out the small passages. In the past we would have said not to do this because you might make the openings bigger. This is still a possibility, but there isn’t any other way to get the passage cleaned. Carburetor cleaner and air pressure will not remove ethanol residue, so the wire is necessary. Just be careful not to enlarge the openings.
The fuel pump could be putting out too much pressure. New pumps are especially suspect. Test your fuel pump and compare with the specification in your motors manual. It would be somewhere between 4 & 7.
That should cover most problems.
If you had an experience with a flooding carburetor, it would be nice to hear what your solution was.