Wednesday, October 19, 2016

Carburetor Balancing Completed With CarbMate

Getting impatient and wanting to move forward I was looking around for an alternative source for the vacuum gauges when I stumbled upon the CarbMate TS-111 in stock at a local racing store (Summit Racing) at a fair price. I have read where other Rotax 912 owners have used this unit to balance the carburetors with good results, so decided to get one on will call and made the drive to Summit and picked it up.
The CarbMate TS-111 carburetor syncing device. A single row of LED’s are used to show the user if the second carburetor has a higher or lower vacuum than the reference carburetor. When both carburetors are synchronized, the green “happy face” LED in the center lights up.

So today the RV-12 was rolled outside and fired up and the CarbMate TS-111 was used to balance the carburetors. Because I decided to use the vacuum ports on the intake manifolds, it was necessary to block off the crossover tube. This is done by flattening the rubber hose from the manifold to the crossover or balance tube. On my newer engine the right side hose is just a little longer than the one on the left side for this very reason. Older Rotax 912 engines require the balance or crossover tube be shortened a little to use the method I used. I want to make a better hose clamp but for the time being what I used did work well. The setup consisted of two pieces of aluminum that were compressed onto the balance tube hose using a C clamp to compress the hose flat thus blocking it off.
C clamp and two pieces of aluminum were used to flatten out the rubber hose on the balance tube to block the balance tube. After this photo was taken electrical tape was wrapped around the components to insure no flying pieces from prop blast should something come lose.

 The CarbMate worked OK … but I still would prefer gauges.  The CarbMate only has one row of LED’s so one carburetor is considered to be the reference and the second carburetor is adjusted to match the “reference” carburetor. When the second carb is adjusted to match the reference carburetor, a green LED lights up in the center of the display showing a “happy face”. So you don’t really know what the actual vacuum is for either carb … only that they match or the second carburetor has a higher or lower vacuum than the reference carburetor. So the CarbMate works well for syncing the carburetors, but is not a good trouble shooting tool like a set of good gauges would be.

Based on the advice of a well-known Rotax mechanic, I used a higher RPM of 3500 to balance the carburetor off idle setting. This is because at 3500 RPM the carburetor is no longer using the idle circuit. The carburetor adjustment for off idle was performed first then the balance was performed at idle. All this took a few cycles of starting the engine then shutting down and making an adjustment and climbing back into the cockpit and checking the results.
As can be seen, at 3,500 RPM I was able to obtain a center green “happy face” on the CarbMate TS-111.

After the carbs were synced, the upper cowling was installed and the RV-12 was taxied over to the on field compass rose to adjust the compass.  What’s next? The sky’s the limit.