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Author Topic:   Tach Match for Evinrude OB
OBouy posted 03-27-2002 09:33 PM ET (US)   Profile for OBouy   Send Email to OBouy  
I'm looking for a tach for my 13 Whaler with a 82 35 HP evindrude, electric start, steering (2 cyl). Can anyone tell me what pulse I would need and other specifics for the proper match? I have the 1/2 moon / 3 leg tach connector on my shifter control.

Thanks for any help!

Dick posted 03-27-2002 10:33 PM ET (US)     Profile for Dick  Send Email to Dick     
My Teleflex tech manual shows that engine to have a 10 pole alternator and a switch position of 5P.
Hope this helps.
OBouy posted 03-27-2002 11:32 PM ET (US)     Profile for OBouy  Send Email to OBouy     
It sure does help..Just what I was looking for.

Thanks alot Dick. Happy boating!

Bigshot posted 03-28-2002 11:22 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You can get the tach that plugs into that connector. I had one on my 82 35hp Johnson. no clue as to what pole setting. i also mounted the tach under the lip next to the light switch. It was more difficult to see but would not fade from sunlight or get wet from spray.
newboater posted 03-28-2002 11:33 AM ET (US)     Profile for newboater  Send Email to newboater     
OK guys maybe you can help me out as well.

I've got an old 2-stroke or 4-stroke OMC tach with my choice of pulses per revolution on the back.

I've got a '75 Evinrude 40 with electric start, dual points, dual coils and some sort of charging magnets/rectifier thingy. Does anyone know how many "pulses/rev" I have, or how to tell based on the information given in the manual?

I chose "3" as I recall, based on what I thought the idle speed was. My first guess was "2", and the tach showed 3000 rpm at idle (clearly not right). I would have thought "2" was the right number.


Dave Smith

daverdla posted 03-28-2002 12:31 PM ET (US)     Profile for daverdla  Send Email to daverdla     
This might help
newboater posted 03-28-2002 12:54 PM ET (US)     Profile for newboater  Send Email to newboater     

Thanks for the link. I think it does help. Although they don't have a setting for my motor, it looks like I may have it wired incorectly.

Dave S.

Bigshot posted 03-28-2002 01:05 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
When in doubt try every setting until one acts correct.
Dick posted 03-28-2002 02:05 PM ET (US)     Profile for Dick  Send Email to Dick     

The Teleflex tech manual shows 12 poles and a switch position of 6. Give it a try.


OBouy posted 03-28-2002 10:10 PM ET (US)     Profile for OBouy  Send Email to OBouy     
It almost sounds as if the formula for this equasion is:

# of alternator(charging)poles/2 = # pulses.

Dick posted 03-28-2002 10:26 PM ET (US)     Profile for Dick  Send Email to Dick     

You are about right, but there are some motors that this doesn't work with and require special tachometers.

newboater posted 03-29-2002 11:16 AM ET (US)     Profile for newboater  Send Email to newboater     
OK guys,

I spent some time with my owner’s manual last night (this is a '75 Evinrude 40hp) and the Teleflex instructions this morning.

The first thing I found in the Teleflex sheet was don't hook up the tach to the ignition system, which I had. I had wired the tach to the low tension side of an ignition coil.

The Evinrude manual says I have one driver coil for the ignition and two for the alternator on the stator assembly.

It also says on the flywheel there are 4 perminant magnets; two of the magnets are the "ignition" magnets, and (I'm guessing) two more for the alternator. It did mention the two ignition magents are of opposite polarity. It looks like there are 3 magnets close together on one side and one on the other side of the flywheel. The manual says the rectifier is a "3-phase design".

I suspect the ignition magnets also provide charging power.

How many pulses or poles do you think I've got?

It seems like each alternator coil would get 4 pulses per revolution, one as each magnet passes. I'm just not sure how the polarity of the pulses gets counted by the tach. Since one of the ignition magnets in the flywheel is the opposite polarity of the other, does tach only count 3 "positive" pulses? I guess it could even two if the alternator magnets are installed with opposite polarities.

I don't see how the motor could have 12 poles or 6 pulses as the teleflex manual recommends. Maybe 8 poles? (2 coils x 4 magnets)

Thanks for any help and insight you can give,

Dave S.
San Diego

OBouy posted 03-30-2002 04:31 PM ET (US)     Profile for OBouy  Send Email to OBouy     

I got a tach and tried 5P.. It seemed high, so I went to 6P.. It seems better.

I finally called a friendly dealer who told me that my engine could have a 2 wire or 3 wire output from alt. The 3 wire is a 3P.. I have that, so I think I've got it.. Need to do a sea trial to confirm..

Try to get the info from a dealer if possible..

newboater posted 04-01-2002 02:28 PM ET (US)     Profile for newboater  Send Email to newboater     
OBouy and anyone else who cares,

I called my local dealer to discuss the tach settings for the '75 40hp motor. He looked in the service manual and couldn't find anything. He said to try a setting of "6", that's what he always starts off with.

I took the tach out, set it to "4" (the max setting on the tach) and rewired it to the rectifier like the Teleflex manual (and the mechanic) said to do. Darn thing didn't work at all!

I read the instructions printed on the tach, and it said "for magneto or battery ignition, wire it to the high side of the points between them and the coil". I guess I had it wired right after all.

I had it set at 2 pulses and I think it's probably correct there based on reading the service manual and how the ignition system works with one driver coil and two sets of points.

Anyhow, not all tachs are wired to the rectifier, that's what I learned.

Dave S.
San Diego

OBouy posted 04-01-2002 10:09 PM ET (US)     Profile for OBouy  Send Email to OBouy     
Alas, I've sea trialed. I started at the 6p setting, but was not convinced I was doing 4700 RPM (28 MPH). The engine sounded too high pitched for that. I went to the 5 setting and it rang out at 5650 RPM at max throttle. I am using an OMC 10.5 x 11 SS prop. I will not run it that high since I believe 5500 is Max desired.

The second number makes more sense to me. I used a brand new digital OMC tach that plugs into the throttle control. I know there is normally a grey wire to hook into, and my tach can do that too. It only has a 5 or 6 setting.

I believe 5 is the correct setting for me, as originally suggested in the first correspondence..

Thanks to all!

Bigshot posted 04-02-2002 10:56 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
5650 is on the money. get rid of that prop and run a 10x13 alum and you will get about 33mph and 5300+rpm's.
OBouy posted 04-02-2002 07:16 PM ET (US)     Profile for OBouy  Send Email to OBouy     

How about if I cup the one I've got since I like Stainless. I just bought this one for $85 to replace the beat up aluminum on the boat. If I could get my money back on it, then I might try the other.

A guy at work runs an 11 or 10 x 13 too with good results.. I don't have trim on my engine (unfortunately), but wouldn't mind a 33MPH li'l runner..

Bigshot posted 04-04-2002 01:23 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Do a double cup which will add 1" of pitch. With a SS 12" should be good. get you down under 500 at least.

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