Hi Terry,
Thanks for your suggestions. The actual symptom was misfiring and not the
vibration due to out of balance carbs. I use the two vacuum gauge method
for balancing and find it works extremely well.
Best wishes,
William
----- Original Message -----
From: "Terry Seaver" <terrys@cisco.com>
Subject: Re: Europa-List: 912 Engine Problem - Request for help
>
> Hi William,
>
> I know this has been beaten to death already, but I feel one more
comment is in order.
> At high throttle settings (open throttle) a difference in the carb sync
(cable adjustment) will hardly be noticed, as small changes in throttle
setting have very minor effect in power.
> At idle, a) the throttle position is set by idle stops, irrespective of
the cable position, so an out of sync condition (cables not adjusted for
identical carb throttle position) would not be very noticeable. Also, b) the
carb balance tube keeps the two sides fairly well synched up to over 2000
rpm, even if the cable sync is not particularly good.
> So, if the cables are out of sync, you will notice it most in the
mid-range, not at idle or high throttle settings.
>
> regards,
> Terry Seaver
>
> William Mills wrote:
>
<combined.merchants@virgin.net>
> >
> > Hi All,
> > Has anyone experienced a similar problem and can anyone help with
suggestions please?
> > On recent flights I have experienced some irregular misfiring when
descending with about quarter throttle and also the occasional hiccup in
cruise, but on my last flight the engine was running so roughly in the
cruise I aborted the flight and nursed it back home.
> > I carried out some tests on the way back. It ran very smoothly on full
throttle, it ran very smoothly on closed throttle, but in between it ran
very roughly. I checked the ignition when running roughly, but there was no
change on either mag. I tried coarsening and fining the prop to see if it
was rpm related, but it wasn't. I changed to reserve tank, but no change.
The carbs are well balanced at tickover and the engine runs smoothly right
down to 1500 rpm. The fuel filters are clean. I can only assume that the
problem is related to carburation, but find it difficult to believe that one
can have a partial blockage, or too much fuel with a needle jet in its mid
range only. As tickover is smooth and roughness stops in flight when
descending with closed throttle, I can only assume that the slow running
mixture adjustment and associated jet are OK. Are there any other jets
apart from the main needle and slow running jet to consider? Although I
never have a problem wit!
> h !
> > starting, can a problem with the starting carb affect the mid range
running only? Can a faulty float valve affect mid range only? My engine
has done about 480 hrs, should I be considering renewing any of the carb
parts as a precaution / planned maintenance etc? I have had a brief chat
with Conrad, but he was unable to put his finger on the problem, so
presumably my symptoms are unusual. He suggested I should check the needles
for wear and the carb rubber mounts / sleeves for splits, which I will.
> > Many thanks for any help,
> > Regards,
> > William
> >
>
>
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