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How (not) to check carburetor balancing / synchronization

  • Arthur Götz
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4 days 7 hours ago #17752 by Arthur Götz
Arthur Götz created the topic: How (not) to check carburetor balancing / synchronization
Dear Forumites

I always thought that pinching the balancing tube between the carburetors of a 914/912 engine is a quick test to check whether carburetors are balanced, or not. When you pinch the tube and the idle goes rougher, the carbs are *definitely* not synchronized. When you pinch the tube and there's no change in smoothness, the carburetors are *probably* balanced.

My AMO disagrees, saying that a rougher idle when pinching the tube says nothing about anything. Everything I thought I knew about why that tube is there just went out the window.

Blue skies
Arthur

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  • Roger Lee
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4 days 5 hours ago #17754 by Roger Lee
Roger Lee replied the topic: How (not) to check carburetor balancing / synchronization
I agree with your AMO.
The only way to really know is put a set of gauges or an electronic device on them. You can have perfectly balanced carbs that have a tad roughness when separated and when you connect them again they are smoother. We humans don't have the fine tuned senses to detect such fine irregularities in things like vibration and vacuum. If it's something you can see, hear or feel then it's usually way out.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
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4 days 3 hours ago #17757 by Arthur Götz
Arthur Götz replied the topic: How (not) to check carburetor balancing / synchronization
Well, it is AMO against AMO. The first one synched the carbs. The engine was a little rough on idle, and I asked a second one to check. When AMO 2 clamped the pipe shut, the idle went from bad to worse, which is when he went "Ah, definitely carb balancing", and reset it perfectly. Now AMO 1 is questioning AMO 2 and I'm sitting in the middle of it all. Well, at least the idle is good now.

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3 days 22 hours ago #17763 by Roger Lee
Roger Lee replied the topic: How (not) to check carburetor balancing / synchronization
Things may have changed. I wouldn't be too quick to point a finger.
The instruments used were not the same one and one could have easily been off. One may have had a leak if they only pinched the rubber tube off. This is why I'm still old school on separating the carbs completely. One may have synced the carbs at different rpms and that in itself at times can be different. If you sync at 2500 vs 3400 rpm there may be a difference. One may have just been more accurate than the other.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
520-349-7056 Cell

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