rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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 Posted: Tue Jul 01, 2014 3:12 pm Post subject: New to Carb Synch in 912. Should Carbs behave the same at a |
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Gordo, You will see some variation at different RPM's than what you used to set the two carbs due to things like airflow differences between the two carbs, manifolds, heads, valve flows, even the amount of oil on the air filters. You can drive yourself crazy trying to chase it down (been there, done that. I once swapped air cleaners after I had balanced the carbs as close as my nice liquid filled gauges would allow, and the carbs were out of balance by over 1" of vacuum. It's a wonder I have any hair left. :-} I did briefly think about making a dedicated flow bench for testing air cleaners after they had been cleaned and re-oiled. Thank goodness the urge passed). Fortunately Rotax put a balance tube the two manifolds. That damps out the small differences once everything is set. If you were to connect to the carb vacuum ports after the balance tube is reconnected you would not be able to find those minor differences.
Rick Girard
On Sun, Jun 29, 2014 at 6:49 AM, Godo Barrenechea <godobcn(at)gmail.com (godobcn(at)gmail.com)> wrote:
| Quote: | Hi,
After attending a couple of seminars and watching the videos, I felt I could run my firts Carb Synch...
I followed the manual and run first the mechanical adjustment followed by the pneumatic ones at 3000 rpm. All good here.
Issue came when, out of curiosity, I wanted to check if carbs would be balanced also at the high rpms when I would be flying, so I started adjusting, not for 3000 as per the manual, but playing up and down.
The thing is that, no matter which rpm I would synchronise for, the results would not be the same all way in the rest of the rpm, so I started to believe that I had a different behaviour in the carbs. I asked the shop that does usually my maintenance and both carbs were cleaned and needles changed 10 h ago.
So here I am, doubting if my readings are wrong, If I need to check again carbs or if I'm only good to build airframes, but unable to tune engines...
For those of you with more experience, any suggestion/comments pls
Thanks in advance
Godo
RV12 in Barcelona, Spain
Last data:
Rigth vs Left Carb mmH reading
4500 rpm +0.5 mm
4000 rpm +0.0 mm
3500 rpm -1.5 mm
3000 rpm -2.5 mm
2500 rpm -2.5 mm
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