First off....an engine quitting in flight does not show any sign of lean etc etc.....
Do your nose up test on the ground after starting the engine and gunning it. If it begins to die...it's too lean, nose down. Richen up. NOse up again....etc until it runs full throttle without dying.
Secondly....check your carb, engine head and back plate screws. Are they tight? If so.....then check the engine liner. OS has improved on the liner...so it may not be that....but the possibility exists.
Thirdly.....check your lines for cracks outside and inside the tank.......installing a new plug does not mean it works. Check it outside with an igniter to see if it lites up.
ONe guy at our club closed his HS needle....and was trying for a half hour to start...until I walked over and started going through the above list. The carb screw vibrated loose etc etc.

Cheers.