Tried this question in the Engines forum but no luck!
Does anyone know where the sweet spot lies with the YS 61 ST2 in terms of peak power output?
I have a Fury Extreme but running 9.3:1 ratio (YS61), a Hatori 90 size muffler (Hatori #996), MAH G2 690mm Blades with CP 15%. I've not run this model for months and made a few changes including dropping out my TJ Pro temporarily after fitting a different gyro since flying it last. I found today that if I put the headspeed at around 1850 to 1900 rpm (17205 to 17670 engine RPM), that the engine sounds as though it starts to hunt and this starts to violently kick the tail from side to side in time with the engine hunting sound. I tried adjusting my needles but this made no difference.
I dropped my Idleup 1 and 2 back to 1760 rpm head speed (16368 engine RPM) and the model again seems settled. Can't see any vibration issues, the model sits like it is on glass when settled and it seems punchy enough too in terms of power. I run my Stratus with YS 91 at 1760 rpm headspeed and it hauls like freight train, but I was under the impression that the 60's run higher headspeeds normally.
The muffler is slightly larger than the 60 size, but this muffler seems to develop better power. My old Zimmerman 60 muffler seemed to 'strangle' the engine somewhat.
Anyone have any previous experience with a similar scenario or does anyone know what is the peak band for ENGINE RPM for the YS 61 ST2 and ball park headspeed for a 9.3:1 60 size model using this engine?