Usually the carb requires a rebuild on the old macs: New fuel pump diaphragm, gaskets, needle & seat, clean the internal fuel filter. Fuel pump diaphraghm on these old saws stretches with age & will not pump fuel. Also check the pressure port to the crankcase, the fuel pump works on a pressure impulse from the crankcase.
If the carb has been apart, and the gaskets & fuel pump diaphragm were removed, chances are they were not "clocked" correctly when the carb was assembled, blocking the ports.
Gasket beween the carb and the crankcase may be installed wrong, blocking the pressure port. Some macs have a spacer and two gaskets between the carb & crankcase, check the pressure port holes and make sure they line up. If the gaskets are hard, you may be leaking air into the crankcase, or the impulse port may not be sealing.
Sometimes the hose in the tank is damaged or the filter on the end of the hose is plugged.
If the saw tries to run when gas is squirted in the carb, then dies, fuel pump diaphraghm is usually the criminal.
