For detailed information on the BING CD-Carburators installed on the Rotax read
this datasheet.
I also think, that you run the Rotax richer than you would run a manually leaned engine in cruise, but as most pilots don´t lean, there is still an improvement.
The CD carburator has the advantage, that it automatically enriches when accelerating, this allows good throttle response although running quite lean at constant power.
As the rotax is a flat 4 with ignition (and therefor intake) order 1 - 4 - 2- 3, always two cylinders at the same intake manifold are filled directly after another in two half rounds of the crankshaft, and then no intake is done for another round. This makes the airflow through the carb pulsating much stronger than for a Conti or Lyco, where all four cylinders draw from the same carb, making airflow nearly constant. Additionally the length of the two intake manifolds for the aft cylinder filled first, and the front cylinder filled second in each cycle are different, this makes the mixture difference between the cylinders even larger than on the Conti/Lycos, and as you can tell if you have 4 EGT probes fittet, is already large for there ones.
Therefor the richest cylinder in the Rotax is running much richer, than the leanest one, requiring an overall richer mixture for smooth running.
Let´s hope Rotax finishes the six cylinder fast, and comes back to the fuel injection for the 912, they already were working on. A few years ago VGS-Motorsport and an italian ultralight manufacturer developed an electronic fuel injection for the 912 independantly from Rotax, and the improvement was enormous. Don´t know why it became no sucess, I believe Rotax doesn´t support the project and did not deliver engines without carbs.
The report is removed from the VGS-homepage now
