Paul,
I think that the problem may be that the tacho coil is picking up
secondary impulses as the speed increases - which accounts for the doubling
of the reading. The Rotax manual does show a graph of the output from the
coil which does show secondary impulses. I suggest that a slight increase in
the gap might cure the problem.
Modellers use a battery operated gadget which works on the strobe effect
of the prop to measure the speed of their props. I bought one when I was
having a similar problem with my tacho, it wasn't very expensive an it did
reassure me that the engine was not in fact overspeeding.
Roger (G-BXTD)
----- Original Message -----
From: "Paul Stewart" <europa@pstewart.f2s.com>
Sent: Tuesday, October 28, 2008 5:48 PM
Subject: Europa-List: Rotax Tacho
>
> Have just run the engine for the first time (914). All seems well with
> exception of rotax tacho. Advancing throttle from 'rough running' to
> just smooth, the tacho jumps from <2000rpm to 4000rpm - numbers which I
> just don't believe. Anyone got any thoughts?
>
> Unfortunately the rest of our engine instruments are a BMA EFIS1 which
> doesn't easily support an alternative tacho for the rotax.
>
>
> Regards
>
> Paul
>
>
>
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