I have a great planes Reactor 3D arf 58" with a OS 55 AX the engine is almost inverted (as the manual shows) it start easely but when you try to tune it feels like a 40 engine (don't sounds like a powerful 55 AX) and when you touch the fuel neddle one click it gets too lean or too reach depending if closing or opening, i try with a tach and it is 2000 rpm below some other 55 AX in the up right position, i'm using 15% omega (Morgan Fuel), 11X7.5 APC prop, # 8 OS glow plug the idle is fine

Thanks
Ruben,J.R.
Venezuela, South America