There is an open space on the top in the back of the motor cowling, where you can grip the motor. It lets dirt into the cowling. Can I close off this opening? Or does it need to be open for air intake, cooling, or some other reason?
That's where the air enters. Strange that dirt should enter, not much dirt on the water. Might it be entering while on the trailer? Dusty and windy in your area? You might consider a canvas motor cover when it's trailered. Or jam a piece of foam rubber in there, just make sure you remove it for running.
