Electric prop

I just scratch-built a plane from the remainders of a crashed Parkflyers.com Cessna 182 and some foam board. I don't have the original prop, because it was destroyed in the crash, so I got a Master Airscrew 7 x 3 prop and stuck it on there. The result: the plane doesn't fly, and the problem is power. I'm pretty sure the prop (which is not a special electric prop) is a major source of the problem. What prop should I be using for a 480 speed plane, not built for speed but not a slowflyer either? Am I right in thinking my 7 x 3 non-electric prop is probably killing me, or do I need to look elsewhere, like drag, for my problem because a 7 x 3 really ought to be fine?