Hey guys... I've got a 70 with a 402 that I just swapped in. My problem is that it has a sort of popping backfire noise under the car when I punch it (Only at WOT). It's got a pertronix ignition set to 10 degrees at base and on manifold vacuum, a single plane edelbrock intake, and a holley 750 double pumper. I fixed a small vacuum leak and played a little with the timing but it persists. Could the power band of the intake (1500-6500 rpm) be a problem? Any suggestions? I've got an old cast iron holley manifold I thought about swapping on. Thanks in advance.