If the carbs are inside a HRC air box then no filter at all is best.

Filter wise though. RAM AIR do some good ones. Foam filters are better than the K&N style ones. Also make sure the end of the filter is foam rather than a metal plate. Get the largest volume ones you can as well.

Wet filters of course filter better than dry ones. Dry makes set up a little easier though and more consistent.
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If I have to take the carbs off once more...