RPM issue, first start, new engine

Hi Rick

From the heavy manual: 

NOTE

The 5th trigger coil is provided for the rev counter

signal.

ELECTRONIC REV COUNTER

On the ignition housing there is an inductive pick-up

triggering one each positive or negative impulse at

every turn of the crankshaft. The optional rev counter

is a specially adapted AC device.

The trigger is a simple  induction coil that can't give that kind of RPM signal.  I think your issue lies with the instrument settings. 

Cheers

I don't think it's an engine issue either. I'm with RW. It's an instrument issue or a bad wire connection or poor ground.

d

Some EFIS/EMS units require some circuitry to filter and clamp the amplitude of the pulses from the inductive pick up. Before you invest a lot of time fiddling about with the engine, can you borrow or buy an analog tacho designed to work with the Rotax 912? If that doesn't work then you know that you have a wiring/sensor fault.

You could make a resistive measurement of the sensor from the wiring connector to make sure that you haven't got a broken wire, you may need to wiggle the wire whilst making the measurement.

If the Rotax gauge works then you may need to investigate adding a resistor in series with the sensor or a zener clamp.

Let us know what you find.

As an example for what Kevin explained, here is the stabilization circuit that Garmin prescribes when connecting the RPM signal to the G3X via the GEA-24. It consists of a resistor, a diode and a zener diode.