In a message dated 7/24/2003 11:34:15 PM Pacific Standard Time,
combined.merchants@virgin.net writes:
> 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.
Check your little hoses that run around the carburetor area. I have a 914, so
I don't know if the system is the same, but I had a very similar problem and
it turned out to be a split in one of those hoses.
Dave
|