I am building a 1/3 scale Balsa USA Sopwith Pup. I have a 32cc Quadra engine that served me well in a 1/4 scale Cub. Would this engine have enough power to fly the Pup? I have been using an 18-6 prop on the Cub, but it turns a 20-6 pretty well too. One of my friends suggested a G62, but I don't want it to be overpowered. I just want it to fly at scale speeds.

I'll bet that's the BUSA kit, right? I've seen that plane fly many times. Trust me, it needs the G-62. Anything smaller just isn't enough. It wallows around and isn't aerobatic at all. Remember, although these planes were slow, they were incredibly aerobatic and quick. That plane has a LOT of drag and needs the pull of a larger prop.

Dr.1

not enough

That statement is the number one cause and effect for the early demise of high drag scale airplanes.