If you have backed the needle way out and it still runs lean then there are two main things to check. First would be a blockage. Take the fuel line off at the carb and the pressure line off at the pipe and blow into the pressure line. Fuel should come out the line VERY easily with little effort. Next would be an airleak of some sort, most likely in the tank. GT tanks can crack and leak air, lines can have holes in them, HSN banjo fitting could be loose, etc.