Denny, as you well know Im a better hand on Deere then AC butttttttttttt heres my own experience as far as the fine old art of "timing by ear"
I find that if a novice run times one by ear they more then likely end up having it tooooooo fast (like your note to slightly retard once done). Its just too tempting to keep advancing cuz they speed up n smooth out so niceeeeee (for a while at least). Kind of like what you mentioned I advancE them to get that smooth RPM increase which I also think is too fast, so then I retard them JUST UNTIL THEY START TO LABOR N SOUND A TAD LOUDER. If they are real quiet thats just too fast Ima thinkin.
ALSO an experienced guy can hear how they start cuz if too fast they tend to bump up against the starter more then they should which can be tough on starter drives.
I also time them some by just setting the start timing n let the advance run where it likes provided within reason. If the advance mechanism is okay n the points are set right, setting up the start timing ougth to get the run timing in the ballpark.
To do that I first rotate the distributor retarted,,,,,,get the engine up to TDC on the No 1 cylinders compression power stroke ,,,,,,,,have the No 1 plug removed but wire attached n side grounded,,,,,,have points gaped correct,,,,,,,turn on ignition,,,,,,,,,,,,,,,slowlyyyyyyyyyyyyyyyyy manually rotate/advance the distributor n STOP when that plug fires........
Any agreement or any response lol
Merry Christmas Yall
John T (Proud owner of an AC D 15 despite my JD buddies makin fun of me lol)