There seems to be a little misunderstanding here on the meaning of "full throttle". Full throttle means the butterfly in the carb is fully open. Mowing, as per instructions, with the engine speed lever in the max position, does not necessarily mean you're operating at full throttle. It just means you're running the engine at the correct design RPM for cutting. The speed lever controls the engine speed, not the throttle opening. Under light load the throttle will only be partly open to maintain the engine speed. If you encounter heavy, tall grass, the governor will increase throttle opening and engine power to maintain engine speed. At that point the throttle can move to wide open and beyond that, the engine will slow or stall because it's wide open but has no more power. The speed lever controls RPM, but the governor controls throttle opening to maintain that RPM. There's no harm in running at a lower RPM when towing, but the blades won't cut too well if you reduce RPM when mowing.