I am posting this for my son. He is working on a 97 chevy at work. He replaced the spider with the upgrade mpfi setup due to the spider leaking really bad. Found a fouled plug, replaced it. Found a bad plug wire, replaced it. Checked extensively for vacuum leaks, none found. He also checked timing, cam-crank at 0, it runs, but backfires thru the exhaust and has no power. What is next?