Wow I just looked up the manual, That poor engine looks like it could die of heat stroke in there(section 3). http://www.hobbyzone.com/documents/HAN4025-manual.pdf Try and fly it without the cowling first.
If it were me I'd cut a slot in the cowl 3/8" wide lined up and right in front of the cylinder, half way to the crank shaft. Than I'd block off the two small holes in front(round and slot) and open it up more to the rear bottom (each side of the muffler). I wonder if anyone else had problems?


Look like an electric prop they used in the picture LOL.