Jamie,

It is hard to tell you exact problem without seeing the plane and engine, but here are a couple of things that happen when your engine sits for a while. First, the tank plug on ARF tanks is made of fairly hard rubber. Many of them get harder and lose their stretch and just fall out. Some get loose and let muffler pressure bleed out of the tank. The worst case is to have the plug come out inside the plane with a full tank of fuel. If you can get ot the tank, grab the plug and brass tubing and give it a tug.

Another thing that can happen is fuel in your needle valve evaporates leaving the oil residue behind. This coats the inside of the fuel jet, changing the orifice size and your mixture setting. As you run the engine again, this slowly washes away and your engine runs fine again. Don't go changing very much except to open the needle a few clicks so you aren't running too lean.

As for the prop, a 10-6 is a little small, but a lot of people run them. It wouldn't be my choice for any .46, but it's in the ball park so if your plane was flying OK before, it isn't the prop. A 10-7 for speed or an 11-5 or 6 for climb power would be a better choice.