Large cooling inlets and outlets do not guarantee good cooling. You must be absolutely sure that any air coming into the cowl actually passes through the fins of the cylinder. If you can see the air outlet, or there's a lot of space around the engine, then air that enters is not likely going through the fins. You'll have to make a baffle to insure that air actually goes through the fins.

That's the most common reason cowled engines don't get enough cooling. From your pictures, it looks like that's exactly what's happening.