Re: Speedometer doest work on Maxum 1700
Most boat speedometers are actually air pressure gauges. There is a tube that runs from the Speedo head to to the transom, there is a connection on Mercruisers (I am guessing but you need to tell us) that runs the tube through the transom and then down the drive to a little hole in the very front of your drive "leg". Actually in the front, above the propeller but below the anti-ventilation plate.
When you are going through the water, at around 15 MPH enough water is being forced into that hole to compress the air in the tube and causes your speedo needle to move. The faster you go, the higher the pressure, the higher the indicated speed. Most report they are horrible inaccurate, but there are some (me included) that have had very good luck with them. There are even some very accurate units used on competition ski boats.
Typically a piece of junk gets in to the leading edge hole and clogs it. You can test by blowing into the tube, or into the speedo head. If the needle moves, then the head is good . . .
This type of system is usually referred to as a pitot. Actually a pitot is the little hole, and for Volvos and many OBs, the "pitot" hangs below the transom, and the tube just goes through a hole drilled through.
Edit: Where are my manners . . . :facepalm: Welcome aboard Nick!!
