The advantage would be that most AVS don't have weird issues as the Avengers do. However some of the smog era AVS carbs are unique to just a year or two and need to be understood to do this sort of tuning.
That said lets see if we can help with the current situation.
Since it idles smooth at 14° 650 rpm your assumption that it has a fairly stock cam seems reasonable.
40° @ 1800 rpm is way too quick. Since its an unknown factory distributor, do you disconnect and plug the vacuum advance hose when you measured this?
Remeasure the timing, vacuum advance disconnected (plug the hose). measure from as slow as the engine will tolerate then every 200 or 250 rpm. This is esspecially important because you are observing a difference in rpm between in gear and out.
The difference between the idle in neutral and the idle in gear is because the load on the engine is high. Its high relative to the power and torque the engine is making at idle speed. That leads us to..
If these are the big sight glass bowls, fuel level should be in the middle.
If these are the small sight plug holes with a clear plug, then bottom as you have done is a good starting point.
With four corner idle and a stockish cam it is very easy to provide excessively rich idle mixture. I'd start with the rear mix screws just cracked open and then adjust the front two for best rpm. Then see if adjusting the secondaries helps at all.
After getting best rpm turn any one screw in just a 1/16 or 1/8. RPM should drop. Turn it back to where it was. Then add 1/8 turn to the screws. The engine needs a richer mixture in gear than in neutral. Its just a PIA to tune with the car in Drive. But the goal is to tune it for maximum efficiency and power in Drive.
As far as using the timing port as an indicator of whether the throttle blades are open too much at idle rpm, that sounds reasonable. However I would not count on that. The carb could have a timing port that is well above .035 or .040" exposure.
View attachment 1715722885
Primaries shold look something like this.
View attachment 1715722887
Secondaries generally less. Often not exposed at all. Leave them at factory setting is often best other than to crack them a little more to see if/when more air is needed.
