Let me make some clarifications here.
Many engines over the history of internal combustion have been air cooled.
The predator engine (along with most small engines like it) are designed with cooling fins, which increase the surface area of the engine, and therefore assists greatly in removing heat.
But what about when it's sitting still? Yes, that's right! The engine was actually DESIGNED to sit in the same spot and run at full load for hours. But how will it not overheat? There's no air flowing over the fins?
It's got a fan bolted to the crankshaft that directs air around the engine. So even when it's being used as the "prime mover" for a generator or a well pump, it still maintains airflow over the cooling fins and stays cool.
Motorcycles don't (usually, as I can't speak for them all) have cooling fans. It's assumed that you're going to be riding it, so you'll do your own wind generation. That's why if I get stuck in traffic on a really hot day, I'll turn the engine off until we start moving again. It saves the engine, and also my goods from getting cooked.
Same story with the Chinese 2 stroke bike engine. Don't let it sit and run without air flow.
(Doesn't apply to liquid-cooled engines)