This heli engine has an unusual midrange issue
At the hover range it has a miss once every 2-3 seconds no matter how rich or lean I tune it in the midrange.
But throttle further up and it gets dead smooth no matter how lean or rich the high end needle is set.

Fuel: 20% Nitro, 20% synthetic oil it's a well known fuel brand and fuel is fresh

Plug: Enya 3 also tried a new OS 8 with the same symptoms.

Any idea ?