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?