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ContinuousWave: Whaler Performance
Faria tach w/1984 Johnson 40HP
|Author||Topic: Faria tach w/1984 Johnson 40HP|
posted 10-26-2002 02:12 PM ET (US)
I have a 13' whaler with a 1984 Johnson 40HP. I have recently installed a Faria tachometer according to the supplied instructions. The tach seems to work fine up to about 3/4 throttle (4000 RPM), but when I go full throttle, the tach drops back down to about 3000 RPM, but the motor is obviously running faster than at 3/4 throttle. I have checked the connections on the tach signal wire on the motor, etc...But can't find where the problem is.
posted 10-26-2002 02:28 PM ET (US)
If you don't get an answer here, go to
http://www.iboats.com and go to their forums. There are a couple of guys there that know that kind of stuff like the back of their hand.
Some whaler owners there, but not too many that I've found. If it is mechanical, great answers!
posted 10-27-2002 02:41 PM ET (US)
Did you have this problem with your original tachometer? Are you sure the pulse setting, on the tachometer, is set right?
posted 10-28-2002 08:40 PM ET (US)
I have contacted Faria regarding the problem that I am having with the tach. I'll see what happens....If they can't help me out, then the tach will go back to the store.
posted 10-29-2002 11:27 AM ET (US)
Change the pole setting on the back of the tach. had the same issue with my 30 Yamaha.
posted 10-29-2002 11:16 PM ET (US)
both provide some background on tachometers and their operation. I think you will find that there is a great deal of information contained in the archives of this website on this topic.
posted 10-29-2002 11:37 PM ET (US)
I have received a reply from Faria....Seems that the setting on the back of the tach was wrong. I had the setting on "5", when it should have been on "4", because I have a 2-cylinder engine. I have changed the setting, but have not had the boat on the water yet to see if it works correctly. I have a flush attachment here, but don't want to try the full-range of engine RPM's with it because connecting rods and pistons/lower unit would probably be spread across the driveway by test completion...Result: More E-Mails such as this one only different topic: engine block replacement.
Will send update once I've had boat on water.
posted 10-29-2002 11:40 PM ET (US)
RE: Did the original tach work???
The original tach got "tatered" about 15 years ago when the boat was "flipped" in salt water. I was about 11 years old at that time.
The motor was entirely rebuilt, but the gauges were not changed out...So I don't know if the original worked correctly or not.
posted 10-30-2002 11:52 PM ET (US)
The tachometer settings correspond to the number of poles in the alternator/charging circuit, which may not correlate with the number of cylinders in the engine.
Even if the tachometer were set to the wrong number of poles, it seems like the readings should still be linear with respect to engine speed.
Did the Faria technician describe why the tachometer readings became non-linear?
posted 11-01-2002 01:48 PM ET (US)
I have the same problem Ė also with a 40hp OMC.
I installed a new Teleflex tach and it worked perfectly the first season. I removed and reinstalled it during revarnishing of the console and since then it has the same symptoms you describe. The tach seems to work fine up to 4000 rpm but the needle stays more-or-less at 4000, even at WOT where it previously indicated 5200 rpm. I didnít mess with the pole settings. Still scratching my head over this one. Iím tempted to buy a new tach and I have the same dilemma about how to test at full throttle in the driveway.
posted 11-01-2002 06:51 PM ET (US)
To river98275 and shookum point, or anybody that can help. I installed a new Faria tachometer in my 13 Whaler with 40 Johnson. I could not get the tachometer to work at all so I had Surplus Unlimited to replace the tach. The replacement had the same problem. After posting questions on this site, I finally found the problem. My tachometer, grey wire, from the motor to the tach. had a bad connection. After repairing this problem the tachometer started working. Like jimh stated, I tried all the pole settings and the rpms are low or high on all settings but number "4". Now here is the dilemma; It to will go to 4,000 rpm and then wander a few hundred rpm. I have a new rectifier but I am going to buy another one and if that doesn't fix it, I plan to replace the stator. I feel sure that we all have the same problem, So lets all be sure to let everyone know what the fix was. I plan to. And, by the way, I contacted Surplus Unlimited and told them the tachometer I was sending back was good, it was my mistake, and I would pay shipping.
posted 11-02-2002 10:56 AM ET (US)
When I was diagnosing some tachometer problems a few years ago I used a $2,500 TEKTRONIX oscilloscope to observe the waveform being produced by the engine and sent to the tachometer. At the time I laughed aloud and thought, "This is probably the first time in outboard repair history anyone has done this."
Most 2-cycle mechanics solve electrical problems with the "easter egg" approach. They just change one component after another until they find the "egg" (the real problem). So if you have a tachometer problem they will replace the tach, the rectifier, and the stator, and maybe the wiring harness. Eventually they hit on the real problem and the outboard is "fixed".
The repair bill is much too high, but the shop manager is smiling, and the poor boat owner usually does not have any other option.
One simple explanation for the tachometer not reading above a certain indicated value is a mechanical interference with the pointer. The meter movement of the gauge may have been damaged and something physically prevents it from reading above a certain point. This seems like a reasonable cause, given the rough motion the meter is exposed to in a boat in a seaway.
Another explanation is the gauge is having trouble reading the pulses from the engine at higher frequencies (i.e., higher crankcase speed).
In this case, there could be several culprits. First, the pulses being produced could be malformed or shaped in such a way that the gauge cannot properly read them. You would have to observe the pulse shape on a oscilloscope to determine if this was a potential explanation or not.
The pulses are generated from a coil or coils arranged to be excited by magnets in the flywheel. The tachometer is generally connected to the coil output, which also feeds current into the charging circuit. The rectifier in the charging circuit clamps the pulse voltage at the battery level, thus the pulses developed are typically 12-16 volt pulses. Problems in the rectifier could affect the pulse shape and voltage. It is a good idea to check the rectifier. Also, I suggest you check the rectifier under hot temperature conditions, as often they fail as the temperature rises.
A second cause for bad readings at higher frequencies could be a problem in the tachometer. It may not be able to properly integrate the pulse stream into a steady current for sending to the meter.
I don't think the circuitry inside a analog gauge marina tachometer is too sophisticated. Most likely the pulse train is integrated into a steady voltage by a simple shunt capacitor. The resultant voltage is "calibrated" by some simple voltage dividers. It is not high science, since the tachometers sell for little more than the price of a quality panel meter of that size.
Ultimately, it may come down to a situation where the motor is working properly and the tachometer is working properly, but they just don't work well together. I am sure if you went to an OMC dealer they would tell you to get an OMC tachometer and your problem would be solved (maybe).
One way to test this theory is to try the two components, the tach and the engine, with other engines and tachometers.
Over the years I have found that the ability of non-technical people to diagnose and repair electrical problems is often vary limited. It is almost impossible to explain simple techniques of diagnosis to a person who does not understand basic concepts of electricity. On the other hand, if you understand basic electricity and electrical trouble shooting techniques you will have no difficulty in isolating the problem by following some of the suggestions I have made above.
posted 11-05-2002 09:54 PM ET (US)
Everyone for all your input on this problem.
I haven't had the boat out on the water in the last few weeks. I have changed the "pole-setting" on the rear of the tach from "5" to "4".
Once I get the boat on the water; I'll post the results.
Thank You All
Justin (aka River98275)
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