Sorry I missed your post,
You know, in my experience I've never had a sticking valve. Good point. In our
automotive troubleshooting that was always a well documented issue, but I've
just never had one in my Rotax. However, you bring up something that is really
important. If the valve on the dual manometer gauges is wide open, the needles
swing just like a sticking valve due to the valve timing and short intake.
Great point. To use the Rotax balancing setup, one has to close the valves
to smooth out the needle movement to get anything close to accurate. John Hurst
had an old dual manifold gauge from a multiengine plane he used for balancing
and it worked perfectly without any valve because of the small orifice in
the gauge itself for smoothing.
The choke valve is another issue I've not had because I made sure I had properly
adjusted my linkage cables. I've also never had a leaking starting carb
gasket.
I did find out from testing the carbs run lean above about 4000 if the
choke cables are pulled.
I know that the pistons in the Bings, when out of sync, will be a bugger to find
with only a vacuum gauge set. I went nuts trying to figure out my slight
roughness
problem about 15 years ago. I made up that plumbers piece to test and
finally found the issue in my plane. I tried cleaning up the walls and pistons,
new diaphragms, and such to no avail. Lockwood advised that I needed two
new carbs. Later when talking to the Rotax factory reps, I was advised that
they actually match their sets of Bing carbs to ensure this was not a problem
with a new engine. I broke down and bought two new matched carbs and it has
been
fine ever since. I know a couple of owners that only changed one carb and
it balanced fine. Were they lucky, or is there a wear issue in the Bings we
don't know about?
I hope one day one of you guys stumbles on how to repair/adjust a set of carbs
that fail to work in unison because of bad pistons. Changing out diaphragms and
gaskets, cleaning and smoothing didn't work for me. Is it geometry, weight,
passages, clearances or what is the actual cause, and what solution is needed
to ensure the carb pistons work in unison has surely escaped me. I never did
figure it out. I threw money at it after nearly six months of tinkering and
my two new carbs worked on the bench in unison and were smooth running.
All one can do is check the compressions are all consistent so you know the
mechanical
is sound, then on to the carbs, to ensure they are rebuilt and work in
unison and then on to the ignition.
You know, it is always the last thing you check that finds the issue. Or you
can
do the car dealer repair method, just change components until the engine runs
right and charge the customer.
Thank you for that,
Bud Yerly
-----Original Message-----
From: owner-europa-list-server@matronics.com
<owner-europa-list-server@matronics.com>
On Behalf Of Area-51
Sent: Sunday, September 19, 2021 8:55 AM
Subject: Europa-List: Re: Carb Balancing
Thanks for the pdf write up Bud; its very thorough informative and extensive,
and
yes will save many going through all those experiences to find a solution...
On the issue of this thread, have you used a dual meter to observe left/right
manifold
pressure readings through operating rpm range and while the vibration
at 3500rpm is active, flickering needle on either gauge will indicate sticking
valve; theres also small chance one of the choke valves is not fully returning
to correct position, or a carburettor piston may be binding intermittently on
the slide... then again it may not be fuel/carbi related.. if you have access
to two verified good carbis then swap them out and see if the issue
disappears...
will be interesting to see what it ends up being !!
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