base timing keeps advancing by itself...

Vacuum advance is disconnected when I set timing, reconnected after. No it does not affect the timing. Unplugging it, plugging it, plugging the disconnected hose to the carb, no effect on base timing at idle. Have to physically twist the distributor.

And to answer all the questions as to balancer slipping... the idle speed does not lie. The way the carb is tuned, I can almost immediately guess within a few degrees where base timing is sitting by the hot idle. 10 degrees idles at around 750 neutral 650 in gear. 12 degrees around 800... 16 degrees around 950ish.. 22 degrees about 1050. The base timing is absolutely, beyond a shadow of a doubt moving around. Balancer is tight and is giving no indicators that it has slipped in any way.