Looking for a little advice on the timing numbers I just pulled from my 73’ Duster (backfire issue)

Mattax said

My guess is too rich when warmed up or oil.

Did the choke fully open?

Also look at the plugs.

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Thanks, looks like I’ll be pulling the plugs next weekend. I believe the choke did fully open but maybe I’ll check again to see if anything is sticking.

If it is too rich is that typically adjusted through the air/fuel mixture screws?