Thanks for the quick reply. The comment about the breather vapors makes a lot of sense, requiring volume to minimize effect on mixture ratio. The flow/volume dynamics would be interesting information, although I might not be able to understand it if presented in engineers' terms. This subject began for me when I picked up a scooter which had no air box. Pod filter alone did not work well. It seems like a tube is needed and tube diameter and length are critical. There's a lot more to this than I thought.
I recently stumbled across an oldish, smallish air cooled Chinese scooter with a very interesting air box. The air box had an original "ram air" intake pipe which I thought should be very efficient - specially at speed. The scooter did not have any brand name or model on it, so I am not sure whether it was a carburetor or fuel injected model. Judging the size of the scooter, I thought it probably came with a 150cc engine with carburetor.
I think while riding at speed air boxes like this will have a bit of pressure inside the box, which could add a pony or two to the engine. Question is whether a standard carburetor can handle such an air box.
A photo of the air box can be seen below.
P.S. Having had a close look at the photo just now, I noticed the scooter had a "Jonway" sticker on it before. Johnway is a well known Chinese brand in our country.
