Mercury water sepperator.

[Duke01]

I installed a 10 micron fuel/water separator (Moeller) last year on my 78 V20 cuddy with 1980 Merc 200. It didn't even have one. Motor runs great, idles good (but won't start unless I use starter fluid - but that is a topic for other thread)

[spareparts]

you should be fine with the 25 micron, 10 micron is for newer fuel injected engines and have become the industry standard. Next time you change the filter, get the sierra 18-7945, usually sells for less than $10