Here is an example of a marine carburetor that looked to be in great condition from the outside, but after removing the top, foreign material was found which was causing the carburetor to flood.
Most marine carburetors are painted black from the factory. This cuts down on potential corrosion.
This carburetor is a Merc 2 barrel.
I often take pictures of carburetors as I tear them down in case I need to be reminded how a part is installed.
You can see the brown foreign material at the bottom of the float bowl. This is the most common reason for a carburetor flooding. Dirt gets into the float metering valve, which causes it to stick open.