I didn’t see any mention of verifying ignition dwell angle in the conversation so far. Dwell is critical to generating spark energy and makes a huge difference in idle quality and spark quality at higher RPMs. If the dwell is too short the spark may be breaking up above 3000rpm, especially if the mixture is on the lean side (harder to ignite). Revving without load wouldn’t necessary show this. Setting dwell is one of the first things I do in a tune-up. If you change it, it will affect your timing as well.

Also, the Loadomatic “black box” can be demystified somewhat if you tee into the distributor vacuum line and bring it into the car with a gauge. Then, you can observe the vacuum reading the distributor “sees” at various speeds and loads. With that data in mind, you can apply vacuum with a hand vacuum pump directly to the distributor and observe the corresponding advance using a timing tape and normal timing light or a dial-back timing light. This way you can get a pretty good picture of what your total advance is on the road.



Regarding the choke stove air intake: how strong does it suck? I agree that it should always be drawing a small amount of air, but usually they draw more air when the engine is cold and less once the choke has fully opened. You can rule out a concern here by temporarily disconnecting the choke, setting it fully open, and plugging the vacuum source to the choke.

Secondary throttle plates that are too far open, or poor alignment/seating of any of the throttle plates in the carburetor could cause some of your idle-related symptoms.

Beautiful car by the way!

1954 Crestline Victoria 312 4-bbl, 3-speed overdrive