Originally Posted by Fenlander
I can only think the air filters would be saturated most of the time.... as in with salty moisture laden air not direct splash.
That's the only reason I can think of. You could make a filter from a non absorbent material though. I guess that even so the environment outboards run in really don't require a filter and that putting one in would tend to vary the air flow more between different conditions and so impact the running.
When you consider the route that the air takes around the outboard as the engine sucks it in from outside, I actually suspect the largest risk isn't from a sand particle that randomly flies in fresh, whizzes around the casing and into the carb needle but instead is far more likely to be a grit particle that is already sitting in the lower casing.
It doesn't seem uncommon to lift the cowl off an outboard and see large amounts of sand, shell and dust/grit sitting on the floor. I'm sure that when a particle does find its way into the carb that it has almost certainly originated from the pile of thousands of particles sitting inside the housing as opposed to one lucky particle arriving fresh from outside.
When I bought that old 15 I sprayed the base with carb cleaner and vast amounts of much came out. Once completely clean and dry I sprayed with lithium grease, my theory being that grit will subsequently stick to that thin layer enough to not be dislodged when the throttle opens up and then when flushing the engine after use I'll flush out the lower casing.
I'd forgotten this practice when I started using the 4 again after years of non use and that's the only time I've had an issue with that engine and found a tiny speck wedged into the carb needle and the engine deck was dirty with loose grit.