You may prefer this to the ball check valve.

Plenty of room for a filter box and filter.

Paul Lamar

Paul,
You like the slide type inlet controls ( throttle bodies) what about a slide
type inlet opening ( rather than the butterfly) - one side open, the other
side filtered, seems simpler to me.
I did consider a filter type butterfly, but thought it might cause too much
restriction when open ( i.e. too thick)
George (down under)

 
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