That all sounds accurate for old oil
The ‘75 harley I got over the summer has castor oil gluing everything down
My mopeds run nothing but full synthetic oil. Never smoke. Only have minimal carbon buildup on the piston crown and very little accumulation anywhere else.
I think running excess of the dino or castor mist be bad. My experience with synthetic is that too much is wasteful, but inconsequential. Maybe a little more crap on the piston crown, but I haven’t tried running a rich oil mix long enough to notice.
What about that 100:1 stuff puchshop advertises all the time? Anyone use that?