Do a search on gas gauge here and read all the info. This has been covered pretty well. I would probably disconnect the battery, pull the sender unit and check the float. Most of the old ones have gone south with pinholes and full of gas.
Take your carb #'s into NAPA and they should be able to get you a standard kit. Try to get the "deluxe" kit if you can. There is a lot of stuff on carb cleaning and rebuild here to search too. Good luck.