912 carb balancing

[kitfox2009]

Today I was installing my new manifold pressure gauge and while I had the carb balance tube off anyway, I decided to hook up a homemade manometer just for fun. I made this out of about 8 feet of clear 1/4 inch tubing and "zip tied" it around a yard stick. I filled about 18 inches of the tube with Rislone. When this is connected to the carbs it showed about 4 inches differential level on the fluid at 2000 RPM.
The question for any experienced 912ers is.
Should this system not be every bit as accurate as the vacuum gauges and electronic devices being sold on the market??
I have not balanced the carbs yet, just wanted to hear comments before I start turning screws. The engine runs great as is --just want to get it even better then great.

Thanks in advance
Don

[Dave S]

Don,

Your home made manometer should work just fine - just remember to check a couple items

1) both tubes need to be separate and open to the atmosphere and unobstructed on the side opposite the manifold connections

2) The liquid levels should be exactly equal with the engine stopped, Since there are two separate tubes - calibration is done simply done by adding liquid to the low one in the static condition till they are level

3) make sure that propwash/wind/drafts are not blowing over the open ends and creating pressure or vacuum on the open end when you are reading


What you are doing is creating a direct reading system - should be bulletproof

Done this stuff in the laboratory all the time. A liquid manometer is pretty much the gold standard - a liquid seeks its own level unless subjected to the influence of a different pressure or vacuum.

Sincerely,

Dave S
KF7
912ULS Warp

[kitfox2009]

Hi Dave
Balanced the carbs today. My two dollar manometer worked just fine. I use just one 8 foot clear tube. Each end is attached to each intake manifold (at the balance tube fittings) and looped around the bottom of the yard stick.I hang the entire assembly from the door lift struts, fasten the bottom end to the unused gear attachment. It is very easy to see the Rislone level. I was quite surprised how sensitive the carb adjustments are therefore it is easy to get the balance right. Just be careful,if things are too far out of balance the Rislone will suck up the tube to the weak carb!! I guess I should have taken some pics!!
Don

[sturdee]

best ever carb balancing tool comes from Twinmax. electronic very simple just disconnect the balance pipe and connect up. easy to check carb balance at any power setting which do vary with cables. worth every penny, ie £59. sight at twinmax.co.uk you wont regret it.

[Renard]

Don, How did you do the balancing - by adjusting the wire that goes from the throttle to the carb?

[Av8r3400]

Don, How did you do the balancing - by adjusting the wire that goes from the throttle to the carb?

Depending on the model and firewall forward, adjusting the cable at the carb is the usual place. In some planes (my model IV-1050 for example) there is a bell-crank assembly under the panel that can be used to set adjustments, too.

[kitfox2009]

Hi Renard

Yes, I completed the mechanical adjustment according to the video on the Rotax site. Then I adjusted the small throttle cable nuts (again according to Rotax video). I found these required very small adjustments in order to affect to manometer levels. Rather than make the all the adjustments with the engine running I found shutting down,adjusting and restarting worked the best. With the manometer hanging in the cockpit doorway it was easy to see from both sides of the a/c.
Mine wasn`t far off balance but it runs very smooth now so I must have done it right.

Good luck Don

[catz631]

Chuck,
If you have the bell crank setup on your throttle you can use a product called a "throttle link " sold at Highwingllc.com. Then with a "Twinmax" or other electronic sync device you can sync your carbs in less than a minute and you don't even need to shut the engine down during the sync process. It's is really slick ! I have had this device on my airplane for a few years now. It's great !
Dick

[cap01]

i agree with catz , the throttle link is an amazing item . eliminates all hassle of adjusting the nuts at the carbs and starting and shutting down the engine a bunch of times . probably takes longer to uncowl the engine than actually adjusting the balance , once your up to temp .