Was there fuel in it prior to adding a gallon?
The idea that the float bowl on the carb was empty, something is preventing the fuel from entering the carb. If you told me there was no fuel coming from the fuel supply when you disconnected it from the carb, then I would suspect there is no fuel to the engine. But you said there was fuel, so the only thing left is the needle and seat. That is what allows fuel in and what stops the fuel from entering.
If you look below, I highlighted the needle and seat. If you take the top of the carburetor off, you will see where the float is attached. As fuel enters the carb, the float raises and presses on the needle and seat. Once it reaches a specific height, the needle seats, and no more fuel enters the carburetor.
What I would do is remove the top of the carburetor and see if it is stuck. Let the fuel supply attached and check if the fuel is allowed to enter the carb with the float hanging down.
Let me know. Also, you may want to consider adding fuel. A gallon is not much. Also, if you left the 2-year-old fuel in it, that can cause it to run poorly if at all.
Let me know.
See pic below.
Tuesday, January 24th, 2023 AT 1:03 PM