I have a YM1700 and the temperature would run from 190-220 while mowing in the summer with a 5' finish mower. On occasion, it would go as high as 230, however, I would usually decrease the engine speed or use a lower gear to keep the temp under 220. The operating temp will all depend on load, engine speed, ambient temperature, angle of travel, etc. In my opinion, the YM1700 has more "engine" than cooling capacity. In other words, you can overheat the engine under the right conditions.
I finally installed a water pump from a YM2000 in order to get around the cooling issue. Now, I have to work it really hard just to see 200. Under the same conditions, it (water pump)dropped the coolant temp by approximately 50 degrees.
Allen