My opinion is that the 'slot' is lean. That is the transition fuel feed between the idle and main circuits. Issues usually show up more with light throttle changes in that area. With more aggressive throttle motion it is quickly moved through and covered up.

And the 4.5 PV is probably too late, too.

My car actually cruises on the idle circuit and slot much of the time. That make tuning a challenge because the idle, cruise, and light acceleration are all happening on the same circuit that is not set up for all that. Most carbs are designed to cruise on the main circuit with the PV circuit being the enrichment for higher loads. On mine, if I set the mix for a clean cruise it is lean enough to have a buck when a little more throttle is applied. If I set the slot mix richer to eliminate the buck, it has a richer cruise ratio than is best.

My car cruises on the mains after about 2,000rpm.

And if there aren't any detonation issues, our engines typically respond well to your rapid ignition advance.