Ok so 2 days ago my '84 would not start at all, I traced it to the Ignition control I went and got a HEI for a chevy truck got it installed and it makes a nice bright blue spark now but the engine just backfires and carries on. The real question is could the HEI have caused a timing issue ? It backfires and carries on like it is out of time. The plug is pretty old and worn so I am going to change it do I use the stock plug type or should it use a different type with the new ignition?