Use a 10x6 prop for starters. Set the high end by starting with the high speed needle valve open about 3 turns. Open the throttle (have your plane well secured and be behind it). Turn the needle valve in (to the right) slowly as long as the engine keeps speeding up. This is usually at around two or two and a half turns. Then open it about an eight turn, so that it slows down just a little bit.

Then while the engine is idling, pinch the fuel tubing to the carb. If the engine speeds up before it quits, the low end is rich. Turn that little screw (with engine not running) in the hole opposite the needle valve one eight of a turn to the right. Restart, and try it again. When the engine quits speeding up when the fuel line is pinched, open the low end screw just a tweak.

If you have to make a big adjustment to the low end, you should re-adjust the top end. If that needed much adjustment, then you should redo the low end again. That should get you pretty close to dialed in.