Briggs and Stratton 20 hp gas problem

Float stuck. Carb gasket missing or leaking.

Float and/or float valve in carburetor? Dirty, stuck, or somehow restricted. To thoroughly clean it you need to remove the fuel bowl, float, and valve, clean them, then reassemble. On MOST carbs with a float, if you turn the carb upside-down and let the float rest on the valve, the float itself should be horizontal. Some engine mfgrs show an actual measurement between the float and the carb casting, but it tends to end up horizontal anyway.

I presume this is a two-cylinder engine, possibly V-twin. I'm pretty sure my old 16hp V-twin generator engine had a fuel pump and bowl. It's important to run the fuel bowl dry at the end of the summer season if you won't be using the engine for the next 6 months or so, otherwise the fuel evaporates and leaves a residue all over everything, usually keeping the float valve shut, so you get no fuel flow and the engine will not run.