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912 carb sync

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jpspencer(at)cableone.net
Guest

Posted: Tue Mar 20, 2007 9:10 am Post subject: 912 carb sync

Anybody besides me have problems with  getting/keeping the carbs synched on their 912. I have the standard  issue 701 throttle arrangement currently but have tried about a half dozen  different setups and have had problems with all of them. The main trouble seems  to be with the off center torque tube actuator which requires a longer cable to  the left carb resulting in a bunch more cable slop on that side. Tried  controlling the left carb off the left side and had problems with that  too.Believe it would be a lot better if could control the carbs from  a firewall center position with equal length cables, and some sort of  "slider" arrangement instead of the torque tube. That would also eliminate  the vertical s turn in the cable required by the stock setup. Anybody got a  "quick easy cheap" fix.

 Joe

 The green one on utube

 85 hours

   [quote][b]

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dirkslabbert(at)telkomsa.
Guest

Posted: Tue Mar 20, 2007 10:52 am Post subject: 912 carb sync

Hallo green one, seen your video, amazing ! is that  a 80 hp 912!?

 I have a different throttle setup, if you are  interested, will send a pic.

 All the best,

 Dirk.

  

  

  

 [quote]   ---

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zsmith3rd(at)earthlink.ne
Guest

Posted: Tue Mar 20, 2007 11:01 am Post subject: 912 carb sync

Joe,



Separate email headed your way to youe email address.



Zed/912/701/etc

do not archive

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larry(at)macsmachine.com
Guest

Posted: Tue Mar 20, 2007 12:05 pm Post subject: 912 carb sync

Joe,

I had that same problem with my Subaru and dual Bing carburetors.  I 

went with a single .065 music wire push-pull wire in a cable casing and 

linked

the carbs together solidly so that they hit stops each end of travel at 

the same time.  Now the throttle acts like one on any Cessna / Piper.

Suggest you go solid rather than cables and remove the springs on the 

carb linkage arms if you still have them.



Larry McFarland at www.macsmachine.com



jpspencer(at)cableone.net wrote:

 	  Quote: 	
		   Anybody besides me have problems with getting/keeping the carbs 

 synched on their 912. I have the standard issue 701 throttle 

 arrangement currently but have tried about a half dozen different 

 setups and have had problems with all of them. The main trouble seems 

 to be with the off center torque tube actuator which requires a longer 

 cable to the left carb resulting in a bunch more cable slop on that 

 side. Tried controlling the left carb off the left side and had 

 problems with that too.Believe it would be a lot better if could 

 control the carbs from a firewall center position with equal length 

 cables, and some sort of "slider" arrangement instead of the torque 

 tube. That would also eliminate the vertical s turn in the 

 cable required by the stock setup. Anybody got a "quick easy cheap" fix.

 Joe

 The green one on utube

 85 hours

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klaus(at)utdallas.edu
Guest

Posted: Tue Mar 20, 2007 2:22 pm Post subject: 912 carb sync

Hi,



The carb sync problem can be solved by doing away with the cables and 

instead

using rods. Rods give positive control, do not require springs, and have

been working reliably for more than 1000 hrs over more than 10 years.

The details are on the website



www.utdallas.edu/~klaus/Airplane/linkage_carburetors.html



Happy flying,



Klaus Truemper



-- 

Klaus Truemper

Professor Emeritus of Computer Science

University of Texas at Dallas

Erik Jonsson School of Engineering and

  Computer Science EC31

P.O. Box 830688

Richardson, TX 75083-0688

(972) 883-2712

klaus(at)utdallas.edu

www.utdallas.edu/~klaus

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ricklach

Joined: 20 Jun 2006
Posts: 127
Location: Kernville, Calif.

Posted: Wed Mar 21, 2007 8:45 am Post subject: Re: 912 carb sync

Hi Klaus,



Your rod design looks very solid and dependable. But I have a question for you. Have you seen any issues with your rod set-up when the engine torques in the airframe. Like RPM changes.



Looking forward to your comments.



Rick

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klaus(at)utdallas.edu
Guest

Posted: Wed Mar 21, 2007 11:14 am Post subject: 912 carb sync

Hi Rick,



Joe Spencer sent an email with the same concern about synchronization

via rods when the engine moves a abit.



Here is the analysis of that aspect:



Altogether, any engine movement is very small

since the motor mounts are so stiff.

But suppose the propeller pulls the engine foward a bit,

or a power reduction has the engine move backward a bit.

Then this effect occurs on both sides, and thus the

throttle settings remain synchronized.  The same conclusion

applies if the engine rotates a bit on the longitudinal axis

due to engine torque. It that case, both throttles are 

again affected the same way.



In fact, we have never noticed

any unbalanced behavior because of power setting or whatever

else might make the engine move a bit. 



It would be different if, looking from the top down on the

engine, the engine would rotated in the mount. But I cannot

see why the engine or propeller forces 

would ever cause such a rotation.



More important is the vibration that constantly shakes

the rods. I was initially concerned that this would wear out

the rod ends and thus lead to imprecise positions of the 

throttle. After more than 1000 hours, there is a tiny amount

of play, of no concern so far. There is NO safety issue since

a large washer is outside the rod end so that even a failure

of the rod end cannot result in the rod disconnecting from the

carburetor. 



My friend Mel Asberry, the expert builder, and I

came up with the rod idea AFTER we had installed the cables.

We never got them to work right and decided to go to rods.

This has been an excellent choice. Once the carburetors

are carefully synchronized, they stay that way and never need

any adjustment. 



 	  Quote: 	
		  From a safety standpoint I never liked the cable setup

to begin with. If one cable disconnects, that side goes to
	


full throttle due to the spring. Yet the other side stays

at whatever setting you have, 

and the engine is extremely unbalanced

in the power output of the cylinders. This has got to be

extremely dangerous. The rods, with their positive control,

completely avoid that problem.



Happy Flying,



Klaus Truemper



-- 

Klaus Truemper

Professor Emeritus of Computer Science

University of Texas at Dallas

Erik Jonsson School of Engineering and

  Computer Science EC31

P.O. Box 830688

Richardson, TX 75083-0688

(972) 883-2712

klaus(at)utdallas.edu

www.utdallas.edu/~klaus

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jpspencer(at)cableone.net
Guest

Posted: Thu Mar 22, 2007 5:17 pm Post subject: 912 carb sync

Thanks guys for the replies on the carb sync  problem. Think I will try Klaus' push/pull rod setup. Will report.

 Joe

   [quote][b]

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