----- Original Message -----
From: "William Mills" <combined.merchants@virgin.net>
Subject: Europa-List: 912 Engine Problem - Request for help
<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 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,
There are those better qualified than I to comment, but I seem
to remember a message of midrange misfiring being caused (eventually) by a
suction leak in the fuel lines - greater effect in cruise/low power, than at
high power - and ground idle unaffected.
FWIW, the difficulty was in finding the leak, as no fuel drips, staining.
Ferg
|