If the carburetor is now clean, including the fuel hose and the needle & seat, there is no more crud in the bottom of the fuel tank, and the engine runs better and better as you run it more, the possibility exists that the original problem is going away. Might have been dirt in the fuel system. Might have been corrosion on the inlet valve or its seat if it's been ridden hard and put up wet. Personally I'd check the ignition timing, and the condition of the points as well if it has any, because you know this engine has been abused by an amateur.
