Yamaha F400A Owner's Manual page 74

Operation
Operating in water containing mud, sand,
silt, debris, or vegetation
Mud, sand, silt, debris, and vegetation in the
water may restrict water flow into the cooling
water inlet covers or clog internal water pas-
sages. Check and clean the cooling water in-
let covers frequently when operating in these
conditions. Flush the engine with clean, fresh
water after use in these environments. Con-
sult your dealer if normal water flow can not
be restored by cleaning the cooling water in-
let covers or flushing with fresh water.
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