Help an old man tune a new to me 340

Spiral core [ also called heli core ] plug leads would be a good idea, not very expensive, if the leads are old or unknown. Eliminates another variable.

No change when the PCV was blocked? There should be. It could jammed. It should rattle when you shake it.
And this is the 2nd or 3rd time I have mentioned this & is so important for your problem: you need to remove the carb & check how much transfer slot is showing above the pri throttle blades. This dimension is fundamental to idle/off idle operation.