Yamaha Speedo - testing operation

[boristhebold]

Ive had some issues with my yamaha 2004/5 speedo not reading speed, cant find bloackage from the intake, it operates from water entering the lower outboard and compressing air in a tube to the speedo unit, the pressure (air pressure) in that tube is sensed by the unit.

My question is, where could I find out what pressure sensed by the unit will activate a speed reading so that with the use of a handheld pressure guage I can test the speedo unit to see if its the actual unit at fault, if its not the unit, and not the input at the engine than my issue could be a blocked, kinked or leaking tube under the deck.

[Poly]

Boris, I’m not sure of the exact calibration but you should be able to get some response with 10-15psi so a bike pump would be an easy way to test if you can bodge a way of joining the tubes.

[Pikey Dave]

Even if you get it to work, pitot type speedos are notoriously inaccurate & unreliable. You're better off using the GPS speed on your plotter.

[willk]

Originally Posted by Pikey Dave

You're better off using the GPS speed on your plotter.

...or even timing how long it takes a chip of wood to pass along the full length of the vessel while underway