My Z28 is a 1971 but it has a newer 350 engine in it (maybe a late '70s). I just replaced all 8 spark plugs and wires. I put in the same brand and type that it had before from the previous owner (Accel 276S spark plugs and Accel 8mm hi-temp wires). Before the replacement I think the engine had a timing issue (it kept misfiring for a couple of seconds after being turned off). The hotter the engine was the more it would misfire. Now with the new spark plugs and wires it is more accelerated at idle speed, it now backfires through the exhaust pipes when I push the throttle, and the throttling is not as strong as it used to be (it doesn't rev up the engine as much). The gap that the old spark plugs had was somewhere around 0.032 inches. The gap that I set in the new spark plugs is 0.035 inches. Can someone shed some light on what's going on and what do I need to do to fix this? Thanks in advance!