Hello, I'm new to this forum but this is my third Aircraft with a 912 ULS. It's my understanding that cruise RPM's 5000 and above uses mainly the Main jet for Fuel/air mixture The needle valve really doesnt come into effect until 2/3third mid range to idle. I believe we all have the same issue during descent and lower RPM's of having our spark plugs running rich. Therefore its safe to say that most of our standard needle jet settings are set to a Rich setting. (No3).Exception for the fellas that are flying at High ASL. It seems that most likely Rotax would want to ensure especially during take off and descent to run rich for obvious safety reasons to prevent fuel starvation.

Anyway, I've been running my Aircraft on #2 neddle jet setting and the engine runs much smoother,  starts better, throttle response great at all ranges and normal mag drop during Mag check. I do not have EGT gauges  but my CHT and water temps stay normal. My plugs run a darker grey but are not white. (After posting this topic I talked to Tech Support about the 2nd clip position and Lockwood aviation said due to a high compression engine they are set up on the rich side and recommended to adjust my Idle air screw a little leaner and return to the 3rd clip. I did do that and re synched the carbs, and leaned out the idle air screw 1/2 turn..  It did help at the lower RPM 's to smoothen out the lower RPM's and the engine is pretty smooth. I guess a little Rich running is better the replacing pistons!! Frank

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