Those motors were great for their time. Light, compact and powerful. They had some vulnerabilities. The cooling system (no thermostat), was designed to just stay ahead of the heat buildup. If the impeller was worn, or the motor was overloaded, it could overheat causing considerable damage. Also, the idle mixture setting procedure is unusual, and most contemporary mechanics are unfamiliar with it. just sayin
Keep the fuel fresh and mixed at precisely 50::1, change the gearoil 1/year, grease her fittings, change the waterpump impeller every couple of years, and she will run very well, for a long time.