Timing Light Accuracy
I've seen 4 different timing lights give 4 different readings. Buy a new, non dial back timing light and if your damper isn't degreed get a timing tape and ONLY use THAT timing light. Let the plugs tell you how much timing you need on THAT timing light. I don't care if it says 20 total or 60 total.
Obviously that's an exaggeration, but I've seen up to 6 degrees difference in lights. Buy a light and use it on your stuff.