Speaking of filters...

...boat I just bought has a Perkins 4-108. I was surprised to see it has
no air filter, only what looks like a flame arrestor. IOW, a metal
screen under a cap. I can't believe this is how it should be, altho the
manual shows this is the part. I'd like to put a real filter on the
intake. Suggestions on where to find an assembly that would fit and be
appropriate?