Boat speedos - how do they work and problem finding

[twr7cx]

I've purchased a boat which has a speedo which doesn't work. Now this is the first time that I have really seen a boat speedo (i.e. only dealt with electric speedos as on vehicles). I've taken a look, and from the back of the speedo gauge there is a clear tube. I followed this tube all the way along checking for any cracks or kinks etc. (there were none), eventually the tube runs to the bottom of the 60HP Mercury outboard. Just prior to this there is a joiner in the tube.
So I removed the tube at the joinery and sucked on it, the gauge moved down. Blew in it (not in the dirty sense) and the gauge moved up slightly. So this says to me that the tube is fine and the gauge seems fine.
Therefore the problem must be in the bottom of the outboard. I did a bit of googleing and it seems there is something called a pitot in there. So can anyone tell me on how to access the pitot and how to repair or replace it if that is the issue?
I'll take photos of the setup tomorrow...

 

[Silvertip]

Re: Boat speedos - how do they work and problem finding

At the leading edge of the lower unit is a very tiny hole (the pitot). It is very common for this hole to become clogged. Clean it out and you will be back in business. A small drill bit, piece of wire, etc., is all thats needed. No need to disassemble anything. Water pressure as the boat moves forward compresses the air in the tube which makes the gauge work. If all you ever worked on is electric speedos on cars, you are a young pup because speedos used to be magnetically operated through a cable driven by the output shaft of the transmission (or off the front wheel if you happened to own a VW Bug).

Boat safely

 

[greggholmes]

Re: Boat speedos - how do they work and problem finding

(or off the front wheel if you happened to own a VW Bug).

Boat safely

that would be the left front wheel. lol they are fun to replace.

 

[bhammer]

Re: Boat speedos - how do they work and problem finding

Yup, you could pull them and wouldn't rack up any milage. of course you didn't know how fast you were going either.

 

[twr7cx]

Re: Boat speedos - how do they work and problem finding

problem solved.

i got a 2mm drill bit and pushed it into the hole. it went 30mm in with no dramas. so i wasn't keen on drilling the hole out since i wasn't sure if it should only go 30mm in.

I then undid the joiner in the tube. Got the air compressor and blew air down the end of the tube. A cloud of dust came out of the end of the motor, and then the air, so the bottom end was clear.

For some reason i then removed the joiner. Turns out whoever installed this gauge hadn't cut the end off the joiner, so it was blocked! I cut this off, put it back together.

And now the gauge works - I tested it with the air compressor.

Cheers for the help and info.

And PS. I've never owned a beetle...