Mercury - 300 Hour Maintenance Kit FourStroke EFI Service Complete OEM Components 8M0113483. Overview. Any boater who puts real time on the water knows that a well-serviced engine changes everything. There's a certain ease that settles in when you've taken care of your outboard - the throttle responds cleaner, the idle evens out, and your mind relaxes because you know the machine beneath you is ready for the next stretch of open water. The Mercury 8M0113483 300 Hour Maintenance Kit brings that k