See what settings you have with your accelerator pump. Bogging or "stumbling" is a sign of a rich condition (gettin too much gas) and popping or backfiring is a sign of a lean condition (not enough gas). Look to the carb first. I can almost gaurantee thats where your problem is. Wouldn't hurt to check the voltage at your coil either. A new coil and wires would be nice too if they are old. I actually had issues with my car when i first got it runnin cause way too much voltage was goin to the coil and frying it. Sometimes my car would run great, other times it would run terrible. A cam shouldn't make your car feel like it has no power, its just gonna shift your torque curve around (unless the lobes are ground off your cam). I'll try to keep an eye on this thread. Anyway, attack the carburetor first. Additionally, i don't wanna be the one to tell you, but you would probably be better off with a 650-675 carb. Smaller carb is a lot easier to dial in. Good luck.