Having a tachometer on board is a very useful thing. It will help the pilot not only to easily tune the carburetor but to monitor the engine in flight as well.
I have received many questions about resetting the Tiny Tach. Please look at the pictures below. The steps are very simple to follow:
Another useful thing is to set the hours after the tachometer has been reset.
In order to do this, the white and the red wires need to be connected to a 12 Volt AC power source. It may be a small bell transformer or other type of 12 Volt AC power source.
The picture below illustrates this:
Remember: The power source MUST be 12 Volt AC
Tiny Tach Troubleshooting
1) No RPM reading:
- faulty spark plug, faulty ignition coil, not enough turns on the red Tach wire
2) Too low RPM readings:
- not enough turns on the red wire (the average is 3 turns)
- faulty spark plug
- incorrectly gapped spark plug electrodes (too much gap); this usually
occurs after the spark plug has been changed; new spark plugs MUST be
gapped to the engine specifications
3) Too high RPM readings:
- red wire too close to the ignition coil
- too many turns of the red wire
- incorrect tachometer type
4) Unstable RPM indications:
- bad connection (the red wire is broken under the insulation) remove
insulation and test - see picture below:
There is another way to test if the red wire is broken:
Set the Ohmmeter to the M Ohm reading.Measure the resistance between the white and the red wire. If the wire is shorted no signal will reach the Tiny Tach. The Ohmmeter will indicate about 5-6 M Ohms.
Shorted wires occur if the wires are routed too close to cylinders, cylinder heads or exhausts. Even with no external damage, I found molten and shorted wires under the insulation.
If there is no reading at all, the wire is definitely broken. The insulator should be removed and the wire soldered.