At that weight, the engine isn't working too hard, but it would breathe better with a different muffler other than that tiny stinger thing. That's an OS 862 or something like that. Swap it out for anything else, or cut the stinger off and open up the hole to about 1/2".
What tank did you use in yours? I haven't messed with a Nobler ARF in a while but always seemed to run into problems getting the tank high enough, and had to shim the engine down.
Type at you later,
Dan McEntee