If you feel that the fuel pump is good and the fuel filter is clean and the fuel lines are clean and no kinks in the rubber hoses for the fuel system then rebuilding the carb is the next step. I would recommend that you do the work yourself, its easy if you follow the rebuild instructions. Don’t strip any screws or brass fittings that require a flat head screwdriver to remove, use the fattest screwdriver that will fit. Pay attention to how to set the float level and replace everything that comes in the kit, don’t over tighten any adjustment screws, if you dent the end of them, they wont work correctly.
Can you give a continuous spray a carb cleaner into the carb air inlet and keep it running, don’t only pour in some gas, that could backfire easier than carb spray and start a fire. If it will keep running then you know spark, timing, and compression are probably all good, time for a carb rebuild or replacement. I am still worried about good fuel supply.
Have you thought of a type of fuel injection upgrade???