Does anyone know what the flap inside the airbox is for. Some say its to let hot air in during a cold start. Some say its to allow more air in if the filter is clogged or at WOT. Could it be the breather for the crankcase? It just bugs me the only 2/3 of my filter is being used. I'd like to take off the flap and the "wall" thats in there but i dont know what its for.

 

They usually direct hot air from the exhaust manifold on petrol engines to aid warming up. They are vacuum operated via a temperature switch in the air filter.