clean the micro screen in the carby, flush out jets and orifices with throttle body cleaner, you can get a pressure can from most auto parts stores.
Fit a carby kit with new diaphragms etc ensuring the needle fork is located into the diaphragm correctly.
Re-set needles to about 1-1/2 turns for low, 2 turns for top.
Tune low end first then top. There are tuning guides online, google them.