On my 73 camaro i put in a hei distributer. it gets go spark to the plugs. The car runs fine but by letting off the the throtle it sound like a timing pop that i hear. i have also replaces all the plugs the wires have it timed at 6 degrees advance. how do i get the popping to stop.

It doesn't sound like an ignition problem, but you might want to check the firing order one more time 1-8-4-3-6-5-7-2. Was the cap new? Are you running it from a good 12V source (not the original power wire)?