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  #1  
Old 05-31-2021, 11:39 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
Posts: 951
Default Carb Sync

Hy Folks.
Having trouble syncronizing carbs that were serviced at Lockwood. Following the instial static adustments, I installed the carb mate for the final adjustments. The carb mate shows solid red left led on the referance carb at 2500 rpm, however at 4000 rpm and up it's centered solid in the green. No amount of cable adjuting will get the reference carb indication off of the far left red led below 2500RPM. What am I missing??
After hours of frustration and I am looking for advice. Thanks....Tom
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  #2  
Old 05-31-2021, 11:50 AM
Taltruda Taltruda is offline
 
Join Date: Oct 2017
Location: Las Vegas, NV
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Default

Isnít the carb adjustment done at idle? I donít think itís possible to have them synchronized throughout the whole rpm range..
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  #3  
Old 05-31-2021, 11:59 AM
Harvey rv12 Harvey rv12 is offline
 
Join Date: Apr 2015
Location: Olympia WA
Posts: 195
Default try 2 manifold pressure gauges

I never had much luck with the carbmate. For me, using the gauges shows the numbers, in-hg, for each carb while advancing through the rpm range. It might show something not seen with carbmate.
YMMV
Tom O.
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  #4  
Old 05-31-2021, 12:45 PM
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rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,453
Default

Though others offering advice here in the forum have focused on balancing the entire throttle range, the focus should be at the low end. Particularly near idle.

The reason is that slight imbalance it higher throttle settings will have very little influence because the throttle plate is open so much and once the balance cross tube is reconnected it will help some as well.

Focus on the low end below 2500 RPM with particular attention at idle and just above idle. Your gear box will thank you.

BTW, I have never like the carbmate much either.
We use a manometer type gauge set but dial gauges are a good choice as well.
One tip is to tie both gauges you are using together with a tee fitting and connect to a vacuum source to make sure they both read the exact same value. If they don't, you can apply a correction factor when you use them, to get more precise with the balance.
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Last edited by rvbuilder2002 : 05-31-2021 at 12:48 PM.
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  #5  
Old 06-01-2021, 08:07 AM
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Piper J3 Piper J3 is offline
 
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Do you have torsion springs on throttle plate shaft? I have both torsion spring and old-style extension spring. The added spring force keeps the throttle cables more uniformly "pulled".

I notice smoother engine throughout entire RPM range...
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  #6  
Old 06-01-2021, 09:14 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
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Quote:
Originally Posted by Piper J3 View Post
Do you have torsion springs on throttle plate shaft? I have both torsion spring and old-style extension spring. The added spring force keeps the throttle cables more uniformly "pulled".

I notice smoother engine throughout entire RPM range...
Hey Jim, You are absolutely correct about the springs. I had been fighting vibration for almost 2 years. I was trying to do another carb balance a few days ago and everything just kept changing and I couldny get a satifactory sync; passable, but not great. There is just too much slop in the throttle cable and that little spring just can't cut it. So I decided to try adding the 3# pull springs and was trying to dial it in again. That's when I couldn't get the guage off of the red peg and I put out a help post here. This morning I went bsck out, determind to fix it. I found that I had a poor hose connection to the carb mate and it must have been leaking some. Anyway, after fixing that and doing another full static and dynamic carb balance everything dialed in perfectly. It hasn't run this smooth in a looooong time. Thanks to all of you for your thoughts.....Tom
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  #7  
Old 06-02-2021, 07:04 AM
bobg56 bobg56 is offline
 
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Location: Peachtree City, GA
Posts: 190
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The stranded cables used for throttle and choke work best when being PULLED. If the SOLID wire cable was used the direction would not matter, stranded cable needs the springs to pull it along, I added the original Rotax spring to my carbs and get a much better sync.
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  #8  
Old 06-03-2021, 05:20 AM
todehnal todehnal is offline
 
Join Date: Jan 2005
Location: Kentucky Lakes area in KY
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Quote:
Originally Posted by bobg56 View Post
The stranded cables used for throttle and choke work best when being PULLED. If the SOLID wire cable was used the direction would not matter, stranded cable needs the springs to pull it along, I added the original Rotax spring to my carbs and get a much better sync.
Hi Bob, I agree that the stranded cables need springs. They pull great, but they don't puch worth a darn. Plus the fact that we are trying to balance these 2 carbs to within a few thousands of an inch of travel, and any slop makes that a challenge. The springs do a good job of compensating for that. I've never seen solid throttle cables on an RV-12. I think that all of the bends that we have in the routing would prevent their use. That being said, these added spring have totally solved the proble. With the added springs, I also now have my RV-12 running smooth again, but it took me a long time to figure that out.
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1998- RV-9 tail kit, built and sold
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  #9  
Old 06-03-2021, 10:03 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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Anyone having trouble with the performance of the torsion throttle springs should be sure they have complied with SB 18-03-06 Rev. 1, which references SB-00026 which details installing VA-00276, Throttle Spring Retainers.
The retainers not being installed, has an influence on the rotational friction of the spring which can effect carb synchronization.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")

Last edited by rvbuilder2002 : 06-03-2021 at 11:34 AM.
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  #10  
Old 06-03-2021, 11:27 AM
seagull seagull is offline
 
Join Date: Dec 2019
Location: San Bernardino
Posts: 344
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Quote:
Originally Posted by rvbuilder2002 View Post
Anyone having trouble with the performance of the torsion throttle springs should be sure they have complied with SB 13-03-06 Rev. 1, which references SB-00026 which details installing VA-00276, Throttle Spring Retainers.
The retainers not being installed, has an influence on the rotational friction of the spring which can effect carb synchronization.
Scott,

I have complied with SB-00026 but your comment about SB 13-03-06 Rev.1 made me think maybe I missed something. I went to the Vans site and could not find SB 13-03-06 Rev.1 with a search or in the SB's.

Can you provide a link?
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