It's probably the float needle valve is stuck in the carb and can't open up to fill the float bowl with gasoline. Modern gas causes that to happen if the carb sits with too long with old gas in it and especially if the tractor sits all winter with the gas tap still turned on... or if it is a leaky tap.
You can take off the carb, clean it up and put a carb kit in it.
Or alternately, do the minimum: Just take off the float bowl, clean up the float valve needle, and reassemble. No kit needed, but you may need a new float bowl gasket.
I do that ot ours nearly every spring. Of course some years I do remember on the last tractor run of the season to turn off the gas and run it until the carb float bowl runs out of fuel. When I do, I don't have to take it apart and clean the carb float needle next spring.