Too add to that when idle speed increases as base timing is adv you need to idle motor back down and recheck the base timing again to ensure it's still at where you just set it.
Thats becasue as idle speed increases the mech adv can become partially activated adding some addtional deg timing to the base timing mesign it up.
Then in that case when you idle motor back down the mech adv deactivates pulling the mech adv timing back out of the base timing that it added at the higher idle rpm which results in the base timing being somewhat retarded.
With that said dont forget to set idle low like 600-650rpm when setting base timing to keep mech adv from partially activating and also ensure you unhook and plug vac adv when setting /checking base or total timing too.
Then when dont setting timing reattach vac adv to full int vac all the time,then reset diel mix and speed too.