Birdseyeview
11-22-2022, 11:51 PM
My 912 ULS seems to be having carb issues again. I'm beginning to dislike the Bing carbs as being too darn touchy.
During todays preflight mag check I noted some minor rough idle at and below 4000 rpm. The rpm drop is at around 200 rpm for both L and R mags (but on previous flights is was more 'normal' at 150 rpm). The ambient temp has been in the 50s lately and everything was running smooth when the ambient had been in the 70s. The engine still runs smooth at WOT and cruise. However, after engine warm up the min idle has also dropped low into the tach yellow zone (less than 1800 rpm) and it wants to die there unless I throttle up a little (2000 rpm ish). The min idle had previously been set at 1800 rpm with very smooth operation there. No external adjustments to either carb or their throttle cables have been made that would account for this drop in idle speed. There is also some hesitation in the engine response when throttling up quickly from idle to WOT during takeoff or in a go-around (never seen before).
I checked the float bowl fuel levels and spark plug appearance after my last flight and all looked very good.
It seems to me that the idle jet in one of the carbs may be fouled, or maybe a needle jet is fouled. The clips on the needles are both in the position #3 groove per the manuals. I'm at 60 hours total time on this engine and it was running great after a new set of plugs a few hours ago. I plan to check the jets for fouling and I'll also check the carb sync. Is there anything else that makes sense to check?
During todays preflight mag check I noted some minor rough idle at and below 4000 rpm. The rpm drop is at around 200 rpm for both L and R mags (but on previous flights is was more 'normal' at 150 rpm). The ambient temp has been in the 50s lately and everything was running smooth when the ambient had been in the 70s. The engine still runs smooth at WOT and cruise. However, after engine warm up the min idle has also dropped low into the tach yellow zone (less than 1800 rpm) and it wants to die there unless I throttle up a little (2000 rpm ish). The min idle had previously been set at 1800 rpm with very smooth operation there. No external adjustments to either carb or their throttle cables have been made that would account for this drop in idle speed. There is also some hesitation in the engine response when throttling up quickly from idle to WOT during takeoff or in a go-around (never seen before).
I checked the float bowl fuel levels and spark plug appearance after my last flight and all looked very good.
It seems to me that the idle jet in one of the carbs may be fouled, or maybe a needle jet is fouled. The clips on the needles are both in the position #3 groove per the manuals. I'm at 60 hours total time on this engine and it was running great after a new set of plugs a few hours ago. I plan to check the jets for fouling and I'll also check the carb sync. Is there anything else that makes sense to check?