Hello SB, here is the engineering. The fins on the flywheel are designed to create a certain (unknown to me at this time) CFMs of ambient air, sucked in through the rope starter, and blown upwards above the rope starter.
This air is channeled by the flattish tins on the rear, side, and front (if so equipped). The air circulates through the TOO SMALL cooling fins on the barrel portion, and head portion of the engine.
The left front opening between the tins is the "exhaust" portion of the airflow design. I have already mentioned the EX. valve and seat being the hottest points of the engine. Now, wherever you would like to take a temp reading, it will NOT be at the hottest point, which ultimately will be the point of failure.
Much time, money and experience goes into the design of the actual shroud, and how much finning, the angles of the fins, even the shapes of the fins, and ultimately the distance between flywheel fins to not burn too much HP, be in balance, and still properly cool the engine for even extreme service.
As I ride in 100+ F temps, the air from that front vent section, at times, is a bit unpleasantly hot on my bare leg (shorts not "skinny-driving").
This engine will NOT get enough passive cooling, as it does not have enough square inches of finning. This was replaced by the fan action so that the engine, no matter how it was used, would not overheat. Idling, pulling hills, or any other activity that increases heat production, without adequate cooling, whether fan-forced, or passive, puts the engine at a higher risk.
I am not saying that the lack of the cooling system may damage your engine, I am saying it Will damage your engine, I just cannot predict exactly when.
I hope this helps all understand the theory, if not, please ask, and I will elaborate, or try to get some engineering data for you.
Mike