There are two little knobs that turn in increments (clicks) to reduce or increase the fuel flow to the carbs. One is attached to the long needle valve and the other to a small nylon valve in the top of the carby. Turning the knobs moves the needle in and out, seemingly to adjust the fuel flow. They are just below the EGT gauges and affect the EGT in the same way a mixture control does. I think they only work at low power, but don't want to screw the engine by turning them the wrong way or at all. I try to use them to keep the EGTs similar and about half way on the gauge, but would like to know what they really are. I find no mention of them in the ROTAX manuals. My students (who own the airplane) tell me the original builder said to put them "5 clicks" out from fully closed and that is where they sit, but it is annoying not to know what they are supposed to do, since they could be incorrectly set as far as I know.