Gasoline reacts with air and water to produce various chemical products. One of the products is a fine particle that accumulates in the fuel system. In very small engines like my Honda 1000i, it is enough to block the carb jets and fuel filter.
I had to disassemble the entire fuel system, scrub, flush, and reassemble before the generator became reliable again.
The deteriorated gas may cause your engine to run poorly or fuel feed system to clog. Some engines are less affected than others.
If it were mine, I would drain the old gas and then try to run it. That will prevent further deterioration of the fuel system. I would also change fuel filter and clean the carb bowl and jets.
Next time use gas stabilizer.
Dutchman Kodiak Cub KD176RD 2018
Nissan Pathfinder 2015