Nice find- and power steering to boot!
Sputtering caused by not enough fuel is common when the inlet/sediment bulb fixture is partially plugged- but it usually happens not long after you start using it. To diagnose, next time it sputters, pull choke out and see if you can adjust choke so it runs good.
But if it ran fine for over an hour, then sputtered, I'd suspect the vent in your fuel cap is plugged. Next time it does it, loosen the fuel cap and see if you get a "whoosh" of air into the tank.
Replacing the fuel cap is one of your easier repair operations. . . LOL