Fuel & Fuel System » Yamaha Maintenance Matters It filters fuel coming into the outboard. This “primary” filter usually features a small water trap at the bottom of the cup. This is the first filter after the 10-micron filter; so if there’s water in here, it’s time to change your 10-micron. On Yamaha outboards, there may be a red ring visible inside this filter Yamaha Outboard Fuel Filters | Wholesale Marine Shop Yamaha Outboard Fuel Filters at Wholesale Marine. Our Yamaha Outboard Fuel Filters are at the lowest prices and same day shipping!