There are many posts regarding clogged carb /main jet. A stuck throttle shaft could act similarly. If this is the Kohler Courage, it is more likely that the float valve is corroded in its bore in the carburetor. Kohler fixes these free for 2 years. Sounds like you need to have it serviced.

This has the 149cc Kohler engine that is manufactured in China. Even thou you serviced the mower with fresh gasoline, there is probably some residual fuel in the carburetor. Chances are the carburetor will need to be removed to clean out the residual fuel. Ask the dealer if a warranty applies since the mower is less than one year old.

If you want to try a quick fix, drain the old fuel by removing the drain plug on the carburetor float bowl. See what happens.