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:
>
> 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 with !
> 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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