Good news is the Ys problem is solved it now stops fine. Gave me a bit of a shock when the engine visibly coughed(but kept running) once during an inverted elevator with zero airspeed but apart from that its going really well. Lots of punch out from the hover and good downline breaking with the 19x8. With 3/4trs of a gallon through it and the valve springs still to be re-adjusted its turning the 19X8W @ 7500. I think this engine is the perfect choice for this plane. Pattern is effortless and hovering is done at half power even with 40% expo on the throttle.