Ramair foam filters flow much better than K&N`s,S&B`s etc.
I`ve used them a fair bit over the years but I`ve also made my own filters from airfilter foam sheets that are readily available from the car tuning shops that spring up everywhere.
A pair of scissors,contact adhesive and old carb to airbox rubbers are all you need to make up your own,it`s far from rocket science.
Mist them with silicon spray before use but not visibly wet or it`ll soften the glue.
My Skorpion runs a pair of Mikuni`s with a `modified` airbox and dual density filter foam I cut to fit an old air cleaner housing,(cut the folded paper element out with a craft knife),flows a treat and is so easy to clean too.
I`ve got one in use while a second is already clean and ready to swap over,takes two minutes.
Had some beautiful spun alloy bellmouths on my 41 mm Dellorto`s that were fitted to my Guzzi Le Mans,topped off with stainless steel laboratory mesh sieves sandwiching the foam that clipped on snugly over their ends,can`t remember the mesh size I used off the top of my head but they worked a treat for years and everyone was always asking me where they could buy some.
This will give you an idea of what I`m talking of:
http://www.tecan.co.uk/sieve/precision_ ... _range.php
http://www.tecan.co.uk/sieve/precision_ ... nefits.php
I can remember my old man using the nylon from ladies stockings over his bellmouths,also remember them being holed now and again by flame `spits` back through the carb if the advance was out on the ignition timing too.
Foam filters are bloody expensive for what they are in my opinion.
,,,,
...i was thinkin bout holding a beer.. 
