I noticed that the YFZ has an air filter that doesn't need the lid to hold it on. My question is what would be the point of getting a pro flow kit if you don't need the custom billet adapter to clamp the filter on? Do I really need to spend the extra cash on it or should I just go buy a filter? Does it help in anyway? Thanks guys.

 

just pop the lid, get a k&n with an outerwear and jet that baby.

 

Yes, the pro flow kit will improve power. You need the plate because when you do the kit, you remove all that stock screen crap and plastic ring that is already in there holding the cone screen there. Then, you put the wider in diameter (better airflow) aluminum ring in there so that you have a lip for the k&n to slip onto, and so theres a lip to fasten the rubber boot onto the other side.
Pretty much what all that means is, you replace all the stock restrictive crap with the, aluminum ring and a k&n,= (proflow kit) and you increase airflow and gain power. Also, it lets you have the peace of mind that you have a positive seal from the airbox to the filter, so your not intaking anything harmful.