Carburator Synchronization

by agustin arango in 912 / 914 Technical Questions 13 years ago

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Re: Carburator Synchronization

by Troy iRMT Enriquez » 13 years ago

Troy iRMT Enriquez

0 7 0

from the beginning.
1st make sure you have slack on the throdle cables.(just enough to make sure the cable is not opening the carbs)do this by adjusting the cable hold where it attaches to the throdle lever on the carbs. make sure the cable cover is centered in its adjustment range.
2nd run engine to temp and check balance.at about 3500 rpm. higher vacume carb needs to be opened more with the cable adjustment screw and lock nut.
3rd once balanced set idle with idle adjustment screws evenly.leave cable length adjustments alone at this point.

Thank you said by: agustin arango, Jez O'Hare

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Re: Carburator Synchronization

by agustin arango » 13 years ago

agustin arango

1 5 0

Thanks Bill

Your explanation helped a lot. The manual should explain what you wrote.

This weekend i will do the Job and will write the result.

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Re: Carburator Synchronization

by carlos montenegro » 13 years ago

carlos montenegro

2 8 0

There is a discrepancy between the Line Man. and the video for the mechanical synchronization and I like to make sure I am doing this right (the video makes more sense to me). In pg 32 section 12-20-00 the step 5 of the mechanical synchronization calls for "1.5 turns counter clockwise" on the idle speed adjustment screw, and the video states "clockwise".

Which is it?

Thanks,

Carlos Montenegro

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Re: Carburator Synchronization

by bill martin » 13 years ago

bill martin

10 757 0

Carlos,

Go clockwise. This way, when you start the engine, you have up to 1.5 turns you can back out counterclockwise to slow the idle if necessary. Once you do the pneumatic adjustment you can set the idle with the idle stop screws on the throttle quadrant. When all is finished and idle speed is set with the throttle quadrant stops, I always like to adjust the stop screw so there is just a little daylight between the idle stop screw and the idle stop when in the full idle position.
This way, you are sure that no force is being exerted on the idle stop, cables, or splitter when you pull the throttle back to idle with too much force.

B ill

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Re: Carburator Synchronization

by Roger Lee » 13 years ago

Roger Lee

125 5.11k 4.51k

Hi Carlos,

You are right it is a misprint in the manual. The correct way is screw it in clockwise to close it then back it out and open counterclockwise to 1.5 turns. If you have a specific issue on one side or the other or you live at a very high elevation this may be tweaked a tad, but for 98% of us it is fine at 1.5 turns out. The black dry soot some see at times is from idling and it isn't there while running at higher rpms.
All aircraft should have a throttle stop in the cockpit so as you can't pull back so far as to bend the throttle stops. There are some planes with a design flaw in this area and I personally believe it should be fix. It is easy enough to do.
The correct way to setup the carb sync for idle is to have your cockpit throttle lever or whatever you have hit its stop at the same time the carbs touch their stop. In the manual this is why you are supposed to use a .004 feel gauge on the idle stop screws and then turn the idle stop screw down to adjust the idle sync. If you leave the idle stop screw not touching then all you can sync is the high rpm range and then you will have an idle out of sync with lots of vibration and you may not even feel it.
Here is another point. I see some sync their carbs at only 2500 rpm. That's too low and too close to idle and the biggest issue is we don't fly there. I never sync a set of carbs at less than 3500 and up to 4000 rpm. The next time one of you set your carb sync at 2500 go ahead and run it up to 3500-4000 rpm and you will see the carbs are not synced and may be anywhere from .5" - 1" vacuum off. That's way too much. The balance tube or cross over tube can handle a little out of sync, but wasn't really designed to handle huge out of sync situations.
We sync our carbs because you don't want one side of the engine trying to run at 5000 rpm while the other wants to run at 5100.(as an example)
Having the carbs synced at idle is very important because that is where more vibration can occur so syncing at idle is very important. Idling at the proper rpm is also very important. If you have a 912ULS then right around 1750-1850 is a fair place to be and when sitting and just idling during warm up or even extended idle waits then 2000+ is better for the vibration reduction. The 912UL can get away with a little less idle rpm because of its lower compression.

We do these things this way to keep our engine healthy for thousands of hours. If you don't like the maint cost now then short time your engine components and pay much more sooner.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Carburator Synchronization

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