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

Mattax said
Good start. Having the rpms with the timing is very helpful.

Zero degrees at idle was for the smog distributor curve.
lets looks at the '73 shop manual and see how your two measurements compare with the timing for a '73 318 (2 bbl of course)

View attachment 1716114540

That looks like this when usin g TDC at 750 rpm. If the engine was set at 2.5BTDC at 750, then shift everything up 2.5 degrees.
View attachment 1716114542

Lets add your measurements to the graph.
View attachment 1716114548

Sure looks like that distributor does not have the original advance curve.

I would try 5* at 750 rpm, then get a few more timing measurements.
Early 318s used 5* initial, so that's certainly safe.

With the 4 bbl, it should be Ok with more advance early as illustrated by the 273 4bbl timing limit
View attachment 1716114554

Wow! Thanks so much for all that information. It really helps me to better understand what happening with my timing and RPMs.

I’m going to try advancing it a bit today. As a newbie to distributors as well is the below circled bolt the one I need to loosen in order to turn the distributor?