Hi!
What's the problem besides "air bubbles"?
You can mount the needle directly on the carb if you like.
But I would first check the tank for leaks.
The Kyosho .40 engine is one of the most Power full sport engines on the market and throttle and run extremely well if set up properly. I run mine on 5% nitro and either 20% castor oil or 15% all syntetic (Motul Micro) and a Nova Rossi 4 glow plug and a 0,1mm head shim or no head shim at all.
That engine turns a 10x6 RAM at 15000rpm (at sea level).