Carb Sync

Hi Sam,

And this is out of the idle circuit. 😊

Just wondering why no one seem to be concerned about throttle cable movement  ie potential for sticking, causing the carbys to be out of balance.

If you don't check balance up/down the engine speed range, how do you assess cable movement ???😈

Hi Sean

The cable movement is what you check in the mechanical checks before the pneumatic sync.  As you note that has to be correct first.  I do agree with Roger and always do it at at least 3000 RPM for the running checks.  If the cables cant track correctly from there to full open then you will be screwed, nothing will balance. I is always a 2 step process of mechanical followed by pneumatic to get it done fully. 

Cheers

I do find some aircraft that don't have very good throttle systems and when you sync them and then throttle back up they aren't in sync and you can chase your tail all day. Some systems just aren't very smooth or return to the exact sync point when the throttle cables move. Unfortunately this is the nature of the beast for some engine throttle setups.

I find the thinner throttle cables work far better and smoother than the thick ones. They just don't bind up in the throttle cable sheath and it allows the throttle arm spring to do a better job.

RW,

"The cable movement is what you check in the mechanical checks before the pneumatic sync"

Can't agree with this advice.

It is during the pneumatic check, that variations between the two carburettors, will be most easily observe.

Cable free, no stick, movement is best assessed when doing the pneumatic balance and at or near flight rpm, BOTH in the throttle increase/decrease action.

RL,

"I find the thinner throttle cables work far better and smoother than the thick ones"

Agreed.

My last aircraft, ATEC Zephyr/912ULS, used what I would describe as motorcycle cables. Lightweight, smooth operation and relativly cheap. From memory, I did one replacement of throttle & choke cables in 20 years of operation.

My Sonex (A) /912ULS uses aircraft grade cables. Much heavier, stiffer & about 10 times the purchase cost, of the above. The only reason this type of cable has been used, is that they came with the almost completed project that I purchased. So far,  2+years and almost 200 hrs , they are working just fine but no better than the motorcycle equivalent. 😈