On Wed, 19 Nov 2008 13:18:54 -0800 (PST), Two meter troll
wrote:

four filters. two sets paired with a y valve so you can run through
one or the other in the set. it would save you changing out filters in
bad weather (which IME is when filters clog up) or while running.

Since he has a single engine usually two switchable filters would
suffice.