Your outboard has a water pressure speedometer located on the lower unit of your motor. From time to time, this feature will get clogged with debris, weeds and gravel. This problem is easy to fix with one simple tool ... a drill bit.
Step 1: Locate the tiny hole on the leading edge of your lower unit. This is where water is forced in and runs to the back of the speedometer, giving you your reading
Step 2: Find a drill bit that fits appropriately into the hole.
Step 3: Using the fluted end of the drill bit, slowly slide the bit back and forth to remove any debris.
This method should take care of any obstructions that may be causing your outboard speedometer reading to be off.
Watch the video below for more information.