base timing keeps advancing by itself...

Throw this in.
When warmed up, idle is higher.
Because the mech advance springs are soft or too long and distributor is already in the curve.
So advances at low rpms. And it may also be aggravated by dirty, hanging pivotal movement. & May not pull back.
Seen it, been there. - but din’t have enough money to buy the t-shirt.

Does the total timing move?, is the important thing.
If that moves, - then something below.
Base timing? - idle well?