Re: [OMC-Boats] speedo and tach

Jeff D,

Trouble shooting your Speedometer breaks down into these basic parts: Pitot pickup, hose, and instrument. This shouldn't be difficult if you go about it in a systematic approach.

One easy test, in the water is to temporarily disconnect the hose from the back of the instrument. Then while underway (get on plane) you should get a small flow of water. If not, start checking for kinks or breaks in the hose line. It's fairly inexpensive to replace the entire hose and replacing the Pitot pickup is fairly easy as well. You can also see if the instrument reacts to apply some air pressure to its input, but be careful not to apply too much pressure.

Tachometers (being electronic) are a little more mysterious to some. Again, let's break it down:

Instrument, feed wire, source.

The source isn't really the coil, per se. It's the action of the contact breaker (points) and condenser opening and closing, resulting in a electronic pulse, which if we observed it on a oscilloscope would look a little like a square wave. So, while the coil is where the easy electrical connection is usually made (on the negative ( - ) side where the points also connect) the coil itself is not the problem if your engine is running fine. And the points are also not the problem. So your pulsing source is no the problem. (You can confirm this by hooking up a cheapo test-tach/dwell meter available at any AutoZone.)

That leaves your gray tacho feed wire and the instrument itself. Troubleshoot the wire path with an ohm-meter or test light for continuity. No brainer there. (Running a new wire isn't particularly expensive.)

Now the instrument, the used tach. It must match the pulse pattern of your four-stroke, V6 engine. Some tach have adjustable DIP switches, some use a rotating selector, depending on the make and model. But usually a misconfigured switch setting would result in the tach reading too low or too high, but still reading something. Go get the installation instructions online from the tach vendor. Once you know what'd your dealing with, it's easy to test it with a short wire, right off the same (-) coil point. Most commonly people have trouble with the mis-configuration of the instrument itself. Alternatively any good automotive instrument shop should be able to test it for you, but you could probably buy a new tach just as cheaply.

BTW, you did a great job on your instrument panel! Keep up the great work and thanks for sharing the pictures.

lee

-----Original Message-----
From: omc-boats-bounces@... [mailto:omc-boats-bounces@...ultimate.com] On Behalf Of jd
Sent: Thursday, August 13, 2009 11:14 PM
To: Evinrude & Johnson Boats of the 1960's and 70's
Subject: [OMC-Boats] speedo and tach

Well i spoke to soon when i bragged about my inexpensive only slightly
used speedo and tach I got off ebay. I had a funny feeling when i
typed that. Neither are working. But it's gotta be something
simple - they're both in great cosmetic shape and how much can really go wrong with either.

For the speedo, can those pitot tube thingys that mount on the
transom get clogged? My is only 3 yrs old and has barely seen
water. I will unplug both ends and do a blow test i guess, but how
can i test the actual speedo gauge?

For the tach, from what i recall it was just a grey wire from the
engine and a ground wire connecting to the back of the gauge. There
was a dial for 4 6 8 and im sure i made sure it was on 6. but if i
got that on 8 or 4 would that make it just not work entirely, or
would it work but give false readings. The grey wire goes to the
coil. But if it was the coil not sending the right voltage down the
grey wire, I would notice other coil related probs wouldn't I?

thanks! Jeff D
_______________________________________________
OMC-Boats mailing list
OMC-Boats@...
http://lists.ultimate.com/mailman/listinfo/omc-boats
Received on Friday, 14 August 2009