Flooding, or a rich condition can be caused by any number of things. Below is a list of things to look for, not in order of importance.
Needle - The viton tip on the needle can be easily damaged while adjusting the float. You should not put any pressure on the needle when adjusting the float. Check if the needle is sealing by blowing into the fuel inlet hole while the float is closed. Air should not get by the needle & seat.
The viton tip on the needle sometimes comes with excess viton residue. This comes off after several starts, but to be sure wipe with mineral spirits to remove the residue.
Is there a gasket below the seat and did the old gasket get removed?
Test the fuel pump pressure for 4 to 4.5 lbs, or as per your motors manual. A new fuel pump is especially suspect. Worst case is to put a regulator between the fuel pump and the carburetor. Excess pressure will hold the needle open.
Test the float. Heat up some water and immerse the brass float. Any bubbles out of the float is a leak. Nitrophyl floats (like plastic) can only be weighed in grams.
Some 2100 carburetors have the rubber check valve in the wall of the float bowl. Be sure the stem is cut off so that it doesn't interfere with the float.
Move the float up and down by hand gently, to see if it catches. A worn float pin can bind if worn.
The power valve might be ruptured allowing excess fuel into the main circuit.
A rich condition can be caused by any of the items above along with the following:
Gas may be getting siphoned through the main discharge. Watch the venturi at idle. Do you see gas leaking into the bore? It should not be. This can be caused by the float bowl vent being plugged off, gas tank vent plugged, venturi gasket not fitting flat, which can hold up the venturi, or perhaps the main discharge not installed correctly. Most have a check weight installed.
Take a look at this page about how the accelerator pump circuit works. There is information there about the main discharge.
Main jets might be too big. This might happen if you installed a different carburetor on the vehicle. The replacement carburetor may not be jetted for your engine.