I currently have a pro design air filter installed on my z400 but i have been hearing great things about the K&N's and i just bought a 2004 stock z400 and am planning to put a full yosh system in in and re jet it but should i get a K&N pro flow air filter or just stick to the normal k&n with outerwear

 

If you run sand only I'd stick with a foam filter because I've seen where K&N will let some sand particles in even with an outerware. (It happened to me- that's why I had to rebuild my motor) If you run dirt K&N all the way.

 

with the K&N you should always run with outerwear on it, no matter where you ride. even with the proflow on it.
and yes it all depends on where you ride for what type of filter you need