FJ1200 1991 Tachometer signal

[Speedy Gramps]

Speedy Gramps        

ANY help please

from last question   "" I read this on one file ""Not sure what year your bike is, but I think on the '91-up models, the fuel pump relay is near the battery on the fuel pump side. It might not be receiving a     tach       signal to keep it operating while the bike is running.
did they mean TECH signal     or    Tachometer signal   ,, because MY  tachometer now does NOT seem to work when it starts .""


OK NOW  NEW question ,, I rebuilt carbs ,, I pulled most electrical connections and cleaned and reset ,  got 2 new,,,, USED coils and replaced mine .

BIKE now starts and runs like it should /////   BUT the tachometer will only move some . (  I. E. )  I rev the motor to 3000 or 4000 and   the tachometer will only move 30  or 40  RPM  NOT  the full  3000  or 4000   SO  does any one have any answers what might cause this to happen  ?? YES  the fuel pump works .


There is  nothing in my Yamaha book about this  ,  that I can find .

[Pat Conlon]

Did the tachometer ever work?

[aviationfred]

Hopefully these photos will help. You want to look at the Grey colored wires


Fred

[aviationfred]

I believe the tachometer circuit works as follows.

The pick up coil sends a pulse input to the igniter unit,
The igniter unit sends an output to the Fuel Pump Relay, Tachometer and Ignition Coil.

You mention that the bike will start and run like normal. This rules out a few things. The pick up coil IS sending pulses, the igniter unit IS receiving the pulses, and the igniter unit IS sending the output to the fuel pump relay, Tachometer and Ignition Coil.

The problem is somewhere from where the grey wire from the tachometer splices into the grey output wire from the igniter unit.

Or, as Pat mentioned the Tachometer itself could be bad. I would also check that you have 12 volts between the brown and black wires going into the tachometer.

Fred

[FJ_Hooligan]

First, determine if the tach itself is getting power.

Since everything else on that Grey Wire circuit is working, I would suspect the connector leading to the gauge cluster.  Might have some corrosion on a few pins.

Good description Fred, but I think what's actually happening on the path that the coil, tach, fuel pump relay and ignitor are on is actually a signal coming from the ground side of the coil. 

The ignitor grounds the Grey Wire leg and allows current from the Red power wire to charge up the coil.  When the plug needs to spark, the ignitor interrupts the ground circuit which causes the coil to fire the spark plug.  So, the ignitor, tach and pump relay see an ON/OFF toggling signal on this circuit.  The frequency of the pulse is directly related to engine speed.