Greetings,
I have 2 YS.91FZ engines that exhibit the same behaviour......they both load up at low throttle openings (1/8 to 1/4 or so). I have the top end set so it's ~3/400rpm from max and the low end returns immediately to and stays at ~2000 (within 100rpm+-). The regulators on both these engines are set flush with the casing. Do I need to wind the regulators in a little on these, or am I doing something else wrong?

I'm using APC 15x8 props on both, with 20% nitro 20% Klotz, and OS#8 plugs.