912 ULS mixture setting
On a recent service of my engine post loss of power on takeoff, I noted the plugs and the exhaust headers had a white powder on them suggesting it was running a little lean. I don't have EGTs on my instrument panel but the CHTs, coolant and oil have always been good temperature. This was not the cause of the issues I was experiencing, but while doing my maintenance and pulling apart the carbs I thought I better set them richer. The needle valves were already on the second richest setting so I put them to the richest setting. I just did a test on the engine today after getting everything reassembled.
The engine is definitely too rich in the midrange now. Between 3500-4000 RPM on a ground runup I am losing about 200 RPM on the top plugs and about 500 on the bottom plugs when cycling the mags. The carb heat also takes about 400 RPM off. However, I am running a constant speed prop and generally have the throttle fully open when flying and bring the RPM back to about 4800 in the cruise. This likely brings the EGTs up compared to running a fixed pitch and throttling back in the cruise. While cruising, the engine seems right on the money. RPM drop with mag cycle is barely noticeable and the carb heat knocks about 50-100RPM off (I disabled the prop controls so this was not compensated for).
I was wondering if anyone else has had similar issues with the 912 being rich in the midrange but good at full power (or as it was before, good in the midrange but lean at full power). Any suggestions for what would be the best way to run it? Thanks!
