LA46. User friendly. You can adjust power with smaller venturi, they will even run on the rich side. Use a free flowing chip muffler or gutted stock muffler. Stock mufflers can also run nice. FP40 or LA40, if you have someone around that can make it work. I looked back over a discussion like this about ARF Noblers powered by an FP 25 or LA25, runs similar. Lots of this and that, back and forth. Then a key number came up, line length. The Nobler was flying on 58' lines. Too short, not optimum. 61' or a bit longer, much better room to maneuver. You will need a 40 or 46 to keep that bird out on the lines when using optimum line length. Even if the Nobler comes in at a lower weight. We have 4 or 5, perhaps more, ARF Noblers doing their thing in our club. Modern 40 (FP or LA, modern, made after 1980) typical power. No 25s. Even the nicely assembled ones. Only ARF Nobler I saw with less power, that worked, was flown by a mythic modeler from Salem NJ area, built first 20 point NATS stunter. SKI Dombrowski (apologies for the probable misspelling). He used a Fox35 that broke from rich to lean whenever the nose pointed up. Short lines. No breeze. Slow laps. Dead calm day. He placed mid pack. Under powering or marginal power leaves little room for mistakes. When the wind blows, doubtful a typical flyer can do a respectable pattern.