Connecting rev counter to 1964 3hp Johnson question

[Monte NZ]

I have an Airguide Rev Counter Model 65S which works well on my 1970 40hp Big Twin which

I have made portable and I would very much appreciate help as to how to hook it up to my 3hp Johnson

A diagram or picture would be a big help.

Thanks in advance.

Monte NZ

[frankr]

Assuming the tach connects to the breaker points on the 40 hp, the 3hp would be connected exactly the same way.  You will have to ren a wire to the points to do that.

[Mumbles]

Are you sure your tach is a model 65S and not a model 653 as I can’t find a 65S listed anywhere in the Airguide Application Guide.  They do show the 653 for two cylinder OMC/Mercs equipped with magneto ignition though, as are your Big Twin and JW motors are.

• This reply was modified 1 year, 11 months ago by Mumbles.

[Monte NZ]

Thanks Frank and Mumbles for your replies.

Frank, I am wondering where I should make the connection on the magneto with the rev counter wire?……….the earth wire is ok and sorry Mumbles, you are correct, the Model No is 653, not 65S

Thanks again

Monte NZ

[bob-d]

You will also have to move the transmitter box as well.

Bob D

[frankr]

You will see two black wires coming out from the under of the 40hp magneto.  They serve other purposes on the 40, among them the ignition switch.  They come from the breaker points in the magneto.  The tach transmitter connects to them, likely at the ignition switch.  Bottom line is, your 3hp does not have those wires and you will have to install one to pick up the signal.  As said, it will be connected to the points exactly like the 40 hp.

[Monte NZ]

Thanks bob-d and Frank for your replies.

I did as suggested and it works!

Thanks again.

Monte NZ by

[frankr]

Great.  Now tell us why you need a tach on a 3hp.  Just curious, that’s all.

[Monte NZ]

Good question Frank… . I was just curious to see what the revs were at idle and full throttle and I thought it would be fun to try it on my other motors too, that I run on my boat.  When I tried it yesterday  in the drum, the slowest idle was 900 rpm,  which I guess is about as low as it will go with compression of only  60 psi on both cylinders.

Thanks again.

Monte NZ

 

[Monte NZ]

In case anyone is interested, attached is a photo of my “portable ” Airguide Tachometer.

https://photos.app.goo.gl/C8zsNCRbxCi6zty29

[Author]

Posts