RB Back fire

Well I have been driving my car for a couple monthes now, but now it back fires like crazy. It will idle fine, but when I put my foot down at all, it just starts to back fire, and misses sometimes. All the wires, and plugs are new, rotor is new, cap new, distributor new. No vacume lines have come off, and the distrubuter is tight and has not moved. New carb, I bought a power valve because my buddie thought that might have gone. I put it in, and nothing. What do you guys think. The motor is pretty much new, and there are more new things on it that used.

Phil