Richard,
There are many things which can cause this problem and you are on the
right track. Rarely does a new Rotax need any tuning, but we tune them
anyway here at Custom Flight, as the factory doesn't quite center speck
the engine to what I call sewing machine smooth... In fact on the last
three engines, my fillings hurt from the factory tune. Not rough, but
not right.
Please check your throttle cables are working together. I will not cut
the cables as the slightest of binding causes a draggy cable. Some use
solid cables, I have a bird flying 10 years on the same stock cables and
it still works like a charm. Check the plugs are all basically the same
with no heavy black soot or white hot deposits. A nice grayish brown
look is right.
Next is the carb balance. We use dual manometers supplied by Rotax
and mechanically set the idle stops using the maintenance manual
procedures, then we pneumatically balance the carbs until each carb is
exactly the same pressure using the Rotax tuning method. Reconnect the
crossover tube and all should be smooth up to 4000 RPM. If you still
have a rough spot, move the needles to the third position.. At full
throttle, and all is well, and when at 3500 or below it runs rough on
the ground please look at your carb mixture. For operations at sea
level to 1500 feet field elevations we have found setting the carb
needle at the third position for both carbs does best at clearing this
rough area. The factory sets one carb normally at position 2 on the
needle and the other on three. This third position is a bit richer and
at part load we get better running at part throttle. If you have EGT,
note the changes on your EGT from side to side.. You can tell if it is
too rich at 4000 RPM if you pull the choke out 1/4 inch and the engine
runs rough and wants to die as (believe it or not) the enrichening
circuit (we call the choke) only works at near idle conditions and
actually leans at 4000 RPM. If the engine smoothly increases or
steady's, then your as rich as you want. I didn't believe this until
Kerry at Lockwood showed me on our 914. Pretty neat.
If your mag drop is 300 or slightly more, you have a mixture problem. I
know, it sounds stupid, but it is true. You may be a bit lean and
moving the needles to a richer setting may be necessary. I'm sure
you're happy to note I have you taking the carbs apart a lot. But once
set, I never have touched mine in three years.
The carb heaters are not the problem, but check for an intake manifold
leak at the rubber gaskets as you said. Of course it will be easy to
tell if you have a manifold leak if you are using the dual Rotax carb
balancing tool with the gauges. I do not use the electric models.
Close the in line valves to get the needles reasonably steady. Good
advice has been given to watching your intake plenum coming loose and
checking for leaks as it causes roughness in the lower 4-5000 RPM
area.... .
Do clean the jets after the engine has sat for a long while for sure and
run the required check of the float bowl plunger so that it shuts off
well. Clean with solvent and low pressure air, not a piece of safety
wire which will scratch the jets and change your settings. Cleanliness
in your tank and fuel lines is a must. I don't even start an engine
until flushing the tank at least three times with fuel, changing the
filters in between and again before test flying.
If she's still running rough look at ignition. Plugs should be clean,
so check your color and compare left side to right.
Hook a timing light to each spark plug lead and idle the engine using a
helper to keep you safe. Watch the light and look for a miss in a
cylinder. You may have a bad coil, unlikely in a new engine, but it has
happened.
Finally, if you have a fixed pitch prop (especially a Warp Drive) and
you throttle back in flight above 80 KIAS, the prop, when windmilling
(being driven by the wind) from high speed sets up a nasty noise and bit
of vibration. It is just like compression braking, and the 912S and
gearbox combo with this prop will tend to vibrate. This is the gear box
lash and turbulence off the prop making the nasty noise and bit of
vibration. This is quite startling to the new Europa passenger. The
Airmaster AP332 will also set up a vibration when compression braking in
a rapid descent by moving the prop from cruise to climb at low power, as
the blade change to a flatter setting sets up a bit of turbulence...
When doing a speed run at cruise of about 140 KIAS, I rarely move the
prop to climb with the power set below 31 inches because it scares the
customers with the sound change and vibration. The comment is usually
"is it supposed to do that!".
Keep us posted. You're on the right track.
Regards,
Bud Yerly
Custom Flight Creations, Inc.
www.customflightcreations.com<http://www.customflightcreations.com/>
(813) 653-4989
----- Original Message -----
From: Richard Iddon<mailto:riddon@sent.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Wednesday, March 07, 2012 2:46 PM
Subject: Re: Europa-List: Rough running 912S
<riddon@sent.com<mailto:riddon@sent.com>>
Hi Guys.
Fuel was drained before layup, bowls dropped and cleaned out. Engine
was left with carbs at full throttle, i.e. minimum tension on springs.
Carbs have been re-balanced before test flight. Ran perfectly on the
ground.
I have rotax permanent carb heaters fitted so that should eliminate
possibility of ice, (I hope!) although humidity was very high for this
particular flight. I had to wait for fog to clear before flight and
temperature and dew point were both 7deg.
I guess I will pull the carbs off, check the sockets and diaphragms,
ensure float bowl vent pipes are OK. Incidentally, I replaced all the
fuel pipes, including the vent pipes, at layup.
Will report back if progress is made.
Richard Iddon.
On 7 Mar 2012, at 08:31, PHILLIPS I wrote:
> Hi Richard
> I would check the free movement of the throttle cables especially if
they
> have been under tension from the return springs for a year, Have you
done a carb sinc? also fuel left in float chambers will evaporate and
leave a gum like deposit
> in the bowl, its worth dropping the bowls for a check,
> good luck
> Ivor
>
> On 7 March 2012 08:10, david park
<dpark748@hotmail.co.uk<mailto:dpark748@hotmail.co.uk>> wrote:
<dpark748@hotmail.co.uk<mailto:dpark748@hotmail.co.uk>>
>
> Weather conditions. - carb ice?
>
> Sent from my iPhone
>
>
> On 7 Mar 2012, at 05:07,
klinefelter.kevin@gmail.com<mailto:klinefelter.kevin@gmail.com> wrote:
>
klinefelter.kevin@gmail.com<mailto:klinefelter.kevin@gmail.com>
> >
> > Where do I look next?
> > Carbs.
> > Kevin
> >
> > On Mar 6, 2012, at 1:23 PM, Richard Iddon
<riddon@sent.com<mailto:riddon@sent.com>> wrote:
> >
<riddon@sent.com<mailto:riddon@sent.com>>
> >>
> >> My 912S hasn't run for almost 12 months. It started and ran well
on ground runs. Test flight was OK although there was some 'plucking'.
Since then I have flown three more times and am finding that the engine
runs fine at full revs or climb settings but when I back off at the top
of the climb, it splutters and coughs a bit and runs quite roughly as if
it is missing a bit. Doesn't fill me with confidence. I have pulled the
plugs and they seem fine, nice even grey colour, no oily plugs. Where do
I look next?
> >>
> >> Richard Iddon
> >>
> >> G-RIXS
> >>
> >>
> >>
> >>
> >
> >
> >
> >
> >
>
>
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