Carb settings without an airbox
My new to me 912UL has individual KN filters. Plane is Apollofox and I have logged 80 hours in 9 weeks, which is much more than usual for me and maybe the reason for an urge to fine tune and tweak. Engine was running less than perfectly smooth I thought, and coming from motorcycles I have seen how going from airbox to KN filter pods can throw off fuelling especially with CV carbs. Generally larger main jets may be required and/or moving the needle clip to one position richer.
So thats what I tried on my 912 too and what I found was my engine runs much smoother in the midrange after moving the needle clips from the Rotax Manual specified 3rd notch (next richest), to 4th position (richest). With the richer mixture it is now more responsive when manipulating throttle on short field landings and stronger too. This is the biggest change. But it appears to run stronger also on top of the RPM range and I had to re-pitch the prop as WOT RPM went from 5800 to 6000. Spark plugs looks great, and not sooty, but exhaust tip colour is dark brown almost black. I have not noticed any change in fuel consumption, if anything it is better now as engine runs more correct now.
Further plan now is to weld in a bung for wide band lambda (oxygen sensor) in the exhaust and see how fuelling look on the AFR gauge. Could be the 185 main jet is too small possibly, but I will not play with it without AFR gauge
Any comments or advice ?
