Speedometer malfunction

[SeaDog46]

I have twin 225 HP Yamaha 4 strokes on a 2005 27' Aquasport. OEM speedometer has stopped displaying mph and trip time yet the Tachs still work. Would appreciate any thoughts on typical causes and fixes. Please advise if more info needed. Thank You.

[fairdeal]

Pitot tube problem?

Actually, how is that rigged on twins... pick one to use, the other gets capped off?

[SeaDog46]

Speed

Thanks for reply fairdeal.........A tube problem certainly sounds quite possible. I understand the theory of how the tubes work but nothing of their use in boats. Problem went from being intermittent but accurate to giving false readings to no readings at all. I wonder if problem isn't in circuitry between tube and meter.

Thanks again.

[fairdeal]

any "circuitry" would be INSIDE the instrument, where the air pressure of the pitot is converted to an electrical signal,

anything can fail, but physical "plugging" of the tube is more common, I think

often right at the hole in the lower unit.

Wire or a small drill bit has been used to gently roto-rooter


btw I'm ASSUMING that we're talking about a standard multi-function gauge and that its fuel gauge and clock are still working.....

[SeaDog46]

Thanks again for your response.........I believe you've probably hit upon the issue. The other functions (clock, fuel) on the gauge work. Looking around there is a small diameter electrical cable that runs from underneath the stbd side of the transom up and into the bulkhead. Just guessing perhaps this cable could be carrying signal from the mounted tube. If so I don't see any way for me to get at it to confirm so I'll just have to add it to the list of maintenance for next servicing. Thanks for your educational assistance.

[fairdeal]

there is a small diameter electrical cable that runs from underneath the stbd side of the transom up and into the bulkhead.

hmmm - that sounds more like a transducer cable - do you have a depthfinder?

the standard Yamaha speedometer pitot tube is built right into the engine - then additional tubing (sometimes black, sometimes clear) is connected by the boat rigger to extend from the engine up to the speedo instrument. That tubing would then be "paralleling" the fuel line, electrical wires, shift/throttle cables. If your engines have "rigging tubes" - probably - a big black "Shopvac hose" that connects each motor to the transom ? then it will be in there, out of sight.

well, sorry I couldn't be more help!

[TownsendsFJR1300]

If its an water pressure, standard speedometer(with Pitot tube), the gauge itself will have a hose (usually black) connected to it....

There's a VERY SMALL hole in the ft of the lower unit for water to enter and while underway, the water presssure will push the air in the tube to activate the speedometer. If used in salt water, the LU tends to clog up unless its flushed..

As noted above, by hand, spinning a small drill bit in that hole may loosen up the crap in there(it is extremly easy to break off the bit in there-not good)

Here's a post I made up re cleaning the entire speedometer system. Works great, cheap. Speedometer has been dead nuts on since being installed;

http://www.yamahaoutboardparts.com/f...g-th23159.html

Even just using the "V" cut hose should help blow it out. Also, in the wire harness loom, just past the engine, the Yamaha black hose WILL have a connector to attach to the hulls hose up to the dash. You can disconnect that and blow/use water to shoot downward and help clean it out..

[SeaDog46]

Hi again fairdeal.......I believe you're right that cable is for the depth/fish finder transducer. Thanks for describing the location of the tube I'll be looking for it in the AM. As you can probably tell I'm fairly new to boat maintenance and care. Been on a lot of boats over the years but this is the first one I've actually owned and had to care for. I really appreciate you taking time to share your knowledge with a rookie.