'92 Marathon Engine Overheating issue

I recently took ownership of a '92 EZ-Go Marathon. The engine appears to be overheating after about 15 minutes or so of driving. It overheats to the point where the plywood seat bottom has a black charred spot that sits over the muffler. It is air cooled...the fan appears to be working, and I pulled the engine cover and there isn't anything that would obstruct air flow from the fan.

Has anyone seen this before and could possibly point me in a direction on how to resolve it?

Thanks in advance.