OS 46 FX Glow Plug Issue
I had this EXACT problem when I first got my OS .46FX. It was leaning out in the air and burning out my plugs. Turned out the needle valve was leaking air leaning me out in flight.
If you can see the lines, watch them at full throttle and see if you see bubbles in the tube going into or out of the needle valve. Into it means you have fuel foaming and just need to balence your prop or pad your tank. Out of it means the valve is leaking.
OS makes a great engine but sucks when it comes to gaskets and seals. Replace the O ring in your valve, make sure all the nuts are tight, and if all else fails, use some liquid gasket (auto parts store) to seal it all up.