Hello all,
On first running my new 912 uls a couple of weeks ago, I got a mag drop
pf just over 500 rpm on one mag and just under 600 rpm on the other mag,
starting at 4000 rpm. All else was OK; oil temp and press, EGTs, CHTs
etc, and the engine ran quite smoothely; even on 1 mag with the rpm
drop it was not obviously rough or misfiring. Prop is Airmaster,
operating correctly - testing done on fine pitch.
Our local Rotax man thought it was probably not a real mag drop but a
tacho problem, though it sounded real. So yesterday we checked it with
an optical tacho and it was real. The optical tacho showed a rpm drop on
the prop from 1700 down to 1490, which is equivalent to a 500 rpm drop
on the engine.
Another rotax owner here suggested it might be the mag ground leads
shorting to the screen, as I had left the screen quite close to the end
of the wire where it enters the ignition modules. So today I stripped
the screen a bit further back, disconnected the screen ground and
connected the mag shorting wires to 2 temporary switches, bypassing the
ignition switch completely. This made no difference, still the same mag
drop, eliminating partial shorting of the mag wires as a cause.
The plug gaps are correct, and the plug colour looks OK. The throttle
cables are set correctly. The engine always starts first go, easily, and
runs smoothly. Our local engineers have no ideas, although they are not
very familiar with rotaxes. So I would really appreciate any advice on
where to go from here - what should I look at next?
Thanks,
Keith Hickling,
New Zealand,
Mono XS, Kit 613.
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