Speedometer doesn't work?

Ok, just the straight stuff...

A marine spedometer is a -very- simple device. It typically has three components: The pitot tube, the hose, the gauge.

Pitot tube: Either a hole cut into the leading edge of the "leg" on an O/B or I/O OR it is often a nylon "finger" that swings down into the water flow, which has a forward facing small hole. The water gets partially into this hole and creates a pressure directly related to the forward speed of the "leg"/pitot. The overwhelmingly most common problem here is something clogged in the hole ( about 1/8" ). Ise a one-sixteenth inch drill bit, and, while twisting it between your fingers, extract the foreign crud. A properly functioning pitot ( with the hose removed ) is a free flowing device. THe alternarte problem is that the hose fell off of the non-pitot end. replace it and clamp it on with a plastic wire-tie.

Hose: a smallish plastic tube that connects to a barbed port on the pitot ( or somewhere on the engine leg ). It carries the pressure generated by the water hitting the openint in the pitot from the pitot, to the gauge. Look for kinks, blockage.

Gauge: this is a very simple barametric metering device ( it measures air pressure ). It has a dial on the front and a hose fitting on the back. If you remove the hose and blow into the hose fitting, the needle should move. If not, you didn't blow hard enough, or the meter is "stuck" ( if meter is stuck, replace ). In the system, the other problem is that the hose comes off of the fitting on the back of the gauge. If so, when you are running, water can be expected to flow out of the hose and the aguge will register some minimum. Make sure the hose is attached and clamp it with a plastic wire-tie.

I hope that helps.
 
I found the drill bit to be a bit scary, and went with a very fine piece of music wire. Sure enough, after some tinkering and low pressure water from the garden hose a piece of sea weed came out. At this point I put the High pressure Garden handle on the hose and blasted the pitot tube. I got the speedo to register 30 to 40 mph. If you trailer your boat, this is the way I would go.

KKKKFL
 
Thanks everyone! I was able to pull the tube off the pitot and blow into the tube and I also used a hand pump with a needle (like one used for inflating a football) and blew into the tube. The speedo got up to about 25 or 30. So, I then checked the small fwd facing hole and used a needle to try and clear it out. I didn't see any obstruction, but I then used the pump and needle again and blew from the spot where the tube connects to the pitot end and blew some air through it to see if it would freely flow through the pitot end...it did. So, I reconnected the tube, then again used the pump and needle on the fwd facing hole with everything connected and pumped some air in there to make sure it was working like it should. The hole was too small for the needle so I just held the needle in front of the hole and got the speedo to register about 30. So, I think I have fixed it! (I hope anyway!) I'm going to the lake on Saturday and I will give it a try then. :D
 
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