Busted Speddometer and Tachometer

I just bought a new (to me) boat, and the speed and tach are not functional. What are your guys suggestions as to how to troubleshoot these to see if its either the guages, wiring, or something in/on the engine itself? BTW, the small intake hole on the foot of the engine is clogged with something (dirt/wood).. Isn't that for the speedometer? Trying to remember back 15 years when I went fishing with my grandfather. I thought he told me that is what it was for one time...I've ordered a owners manual from Merc. for the engine, but it hasn't come in yet.<br /><br />Thanks,<br />Dave

Re: Busted Speddometer and Tachometer

The small diameter hole on my 60 Merc was plugged with what looked like wet wood pulp preventing the speedomoeter from operating. I tried several ways to remove the debris, but in the end this is what worked: <br /> <br />Using a hand pump, hook up an open end of the speedometer pitot tube on the lower end and apply moderate air pressure. I found that the attachment used to inflate water toys fit into the pitot tube well. Find the appropriate size drill bit to fit in the pick-up hole (3/32"), and rotate it with your fingers when inserting it into the hole. When it is in as far as it will go, begin to pull it out while applying the air pressure. The flutes on the dril tend to grab onto the debris, and should pull the debris clear from the hole. The air pressure helps to pursuade it, and you be greeted with a rush of air as the debris finally pops out of the hole.

Re: Busted Speddometer and Tachometer

Thanks AMD. I've done half of your suggestion, rotating a 3/32 bit by hand in the intake hole. I've cleared out a fair amount of the debris. My question now is (fixing to show my newbie ignorance), what it the pitot tube, and where is it located, so that I can force some air through it?<br /><br />Thanks,<br />Dave

Re: Busted Speddometer and Tachometer

There should be a piece of tubing running up inside the lower end, and heading towards the dash console. Water enters the little hole in the lower end, and creates pressure in the tube (pitot tube). Thats pressure is what makes the speedo needle move. Somewhere along there it should have a connector that can be pulled apart (near the motor). Take the connection apart, and blow into the part that is attached to the motor, while trying to remove the debris.<br /><br />Also, you should be able to blow gently into the end attached to the speedo and see the needle move. The tubing deteriorates over time, and may develop leaks or be pinched in such a way as to render them ineffective. Pitot tube is cheap, and quite easy to replace completely.<br /><br />Get the hole, and tubing cleaned out and go from there.<br /><br />Note: This is assuming your speedo is connected to the motor. You may find that an external speedo pickup is connected to the transom of the boat instead. Is is normally mounted at the rear bottom edge of the boat on the right side. Looks like a hinged lever assembly, with a pitot tube connected to it. <br /><br />Both methods are popular, and you could have either one.

Re: Busted Speddometer and Tachometer

Thanks AMD.

Re: Busted Speddometer and Tachometer

Clarification: the hole in the lower unit IS the "pitot tube" and is the same functionally as the pitot tube on an airplane, where it is a forward facing tube affair. The gauge on the dash is just a pressure gauge measuring the impact pressure on the "tube".<br /><br />Now the tach is electronic and when it doesn't work often suggests the rectifier/regulator is not working either. I would suggest getting a shop manual [OEM only] to trouble shoot.

Re: Busted Speddometer and Tachometer

You guys forgot the obvious mabye an elec acc switch , none of my guages work until i hit mine