C40TLRX tach output signal

[99yam40]

I would like to find out what kind of a signal the tach receives from this Yamaha C40TLRX motor and how it is translated to RPM.

I do not have a tach but have a Fluke 87, and would like to read the RPMs for testing and trouble shooting. From what I have found out so far is it is a AC voltage signal from the 6 Pole alternator, but I do not know and have not been able to find out if it translates the voltage increase directly to RPM or if it uses the pulses(Hz), or a combination of voltage level and pulses.
Could the signal be read by a Digital VOM to represent the RPM? If so, does anyone know what the ratio would be?
0-? volts = 0-? RPM
or ? Hz= ? RPM

 

[99yam40]

Rodbolt

Rodbolt

Rodbolt, could you give me some of your expert knowledge on the Yamaha tach signal and operation.

 

[99yam40]

Re: C40TLRX tach output signal

Well, I gave up on going in this direction and bought a ESI #321 EZ tach on line. I found out it does not work with these CDI outboards, the EMI causes them to go crazy.
Had to send it back and it cost me a 20 percent restocking fee and shipping.

But I did find a unit, with the help from Steve from ESI, that is new from ESI it is their ESI#328 EZ Tach +Plus sold by Matco Tools for now, that works well on outboards along with most other motors 2 and 4 stroke with spark plug wires.

It is a wireless unit you just hold close to plug wire or coil, and has a wire with a clip (kind of cheap looking)that plugs in to unit to extend around the motor to use while running on the water. I tried it out yesterday and I finally found out that my WOT RPM is 5500 . So, I finally know that my high speed cut out is not from hitting the Rev limiter.
You do have to be careful that to keep the wire away from the other coils and wires or it will pick up multiple signals from them also and give strange readings.