Hi!
The OS line of FP and LA engines are very user friendly and need hardly any any adjustments on the air-bleed needle to function extremly well.
They throttle and run perfect from the start if you just follow some simple rules.
And here they are:

Use fresh fuel containing 5-10%nitro...15% is over kill!
Use an OS 8 or Enya 3 glowplug (There are many other god plugs too).
Use a 10x6, 11x5 or 11x6 prop. Preferable APC, RAM , Bolly or Graupner.
Use a 240cc (8oz) fuel tank with it's center line inline with the carb when plane sits horizontal (very important).
Do not use a cheap plastic spinner without a backplate. Instead use an aluminum spinner nut.

If you do the above and just set the engine a little rich your engine will run and throttle just fine.
But if not you must check the backplate screws, head screws, carb, fuel and glowplug.

Regards!
Jan K
Sweden