Personally, I'd leave it alone / no filter is necessary or beneficial if it didn't have one from the factory.
The Yanmar guys have sold hundreds of thousands of those engines.. The engineers know what they're doing. How much dust is in suspension in your enclosed / damp engine room? If you introduce a filter you impede the flow of air and change the fuel / air ratio : You create a fuel rich mixture. The simpleton mechanical fuel injection systems on those things has no idea that anything has changed. No computer control / MAF system like your car here. Whatever it was set at originally is where it sits for ever. Those engines are bad enough on carbonizing due to the fact that they live an easy life on a sailboat, you don't want to make the situation any worse. My 2 cents... Francois Rivard 1990 34+ "Take Five" Lake Lanier, GA
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