Erratic reading tach on 1976 evinrude v6 200hp

Hi everyone!
I am currently restoring a 1971 19' Orlando clipper fitted with a fully rebuilt 1976 evinrude v6 200 hp. As I got in to the electric dept., i got everything working nicely except the tach. On idle it does not read anything and if you rev the thing it comes up to about 4500 rpm's and the engine sounds like 10000 rpms!
I checked the rectifier and the charging system and i have 13v at idle. I checked ground and 12v to the tach and ot them. I have my doubs on the dial in the tach it says 2, 4, 6, 10, 12 poles.
I would really like to have an accurate reading on the revs because I'm thinking about moving to a higher pitch prop than the 15" x 16" that i have now.
I would apreciate any help!!
Thanks!!

Re: Erratic reading tach on 1976 evinrude v6 200hp

Welcome Hanielj to iboats.
The tach should be set on 6 poles. Give that a try and let us know if that corrects the problem.

Re: Erratic reading tach on 1976 evinrude v6 200hp

Good evening Jimmy!
Thanks for the quick reply!
I went there right know and checked and the tiny arrow is pointing to 6 but i noticed that my tach has two posts for the signal .
One says J/E and it has a sticker with something about "evinrude sender"
The other post just says "send" and the sticker says "alternator"
Right now it is in the J/E post.
Is that right? , this tack must be more than 30 years old i bet it is the one the boat came with LOL!
Thanks!

Re: Erratic reading tach on 1976 evinrude v6 200hp

Good evening,

No, It should be on the alternator terminal.
The other terminal is for the way earlier years that required a sender at the motor.
Post back your results.

Re: Erratic reading tach on 1976 evinrude v6 200hp

Hi Guys!
I just arrived from 8 hrs in front off a computer (job)
and went and changed the signal wire ( gray ) from the J/E terminal on my
tach and put it in the alternator post. Started the thing and i noticed that it seems to read about right in idle ~1000 rpms but is i just touch the accelerator a bit it went all the way to 5000 rpms!. The motor may have been at 1200 - 1500 rpms. Tried changing the dial thing to 4, 10 , 12 poles and the same. I took the bonnet off and checked the wire strip and noticed that the previous owner had apparently redundant voltage regulators. I have the one that goes just next to the wire strip and the other one ( i assume the older ) which goes on top of the power head. Now The tach is attached to the cable coming in from that last voltage regulator. Could it be that the one on top is faulty. It is dripping a gluey brown substance from underneath it. The thing is that my voltmeter as well as the boat's both read 13v at idle and 13.6v accelerating.
Would changing the cable to the bolt where the other rectifier correct the problem?
Any help i would appreciate.
Many Thanks!!

Re: Erratic reading tach on 1976 evinrude v6 200hp

What you should have is an unregulated rectifier (triangular with a cylinder on top) and a six sided regulator. Potting coming from either one indicated that they have overheated and are probably not functioning.

If the rectifier is the one that has melted, you should disconnect it now because if the diode wires fuse it will allow battery voltage to reach the stator and damage that as well.

There are many different tachometers, most have the manufacturers name on the face of the dial in very small letters and many have a model number; look just inside the lense.

Re: Erratic reading tach on 1976 evinrude v6 200hp

Good evening ezeke
I checked and othe Potting is coming from the one on top of the power head, i think is is the 6 sided one. The voltage of the batery seems ok though even with nav lights on and bilge pump on 12.5V at idle 13v accelerating. Is that ok? Should i change the one dripping putty? Would that correct my tach?
I should keep the boat dry until i get this sorted out right?
Many Thanks!!

Re: Erratic reading tach on 1976 evinrude v6 200hp

I would guess that the regulator has failed, but it's hard to say from what information we have.

The unregulated rectifier would show higher voltage with no load on the system, increasing as the RPM of the engine increases. You can test the rectifier diodes with an ohmmeter using Mr Reeves' instructions in the Engine FAQ forum: http://forums.iboats.com/showthread.php?t=190638

Map the wires on the rectifier before removing for testing so that you can put them back the way they were afterwards.

The rectifier is the device that converts the a/c voltage to D/C voltage by the use of blocking diodes. It will be similar to the one in the picture:

Re: Erratic reading tach on 1976 evinrude v6 200hp

The 76 200 had a cover plate over the water cavity on the top of the powerhead. Part number 318473. Possible that the engine may have been overhauled at some point and the original plain aluminum cover may have become lost. Someone just used the newer style regulator as a dummy to fill the hole. Make sure it is not connected. You should be running the small triangular rectifier only-as mentioned by ezeke. Your system should read battery voltage of 12.5 or so before you start the engine. After running it for 1/2 hour or so, the rectifier should recharge the battery and voltage can creep up to between 15-16 volts and is normal. The rectifier serves two purposes: charges the battery and sends the signal to the tach. A bad rectifier will show up in erratic tach readings, then later the battery can go dead from lack of charging. Also possible you have a bad grey tach lead. You can run a temporary replacement one from the terminal strip on the starboard side of the engine-in place of the existing grey lead- to the tach under the dash-then see if it makes a difference. You may be happier with a different prop, try a 19 pitch prop and then check your rpms.