If the timing is to far advanced, like 35 + deg BTDC then it may develop a HS speed miss, almost like it is to rich. BUT you can't tune it out using the carb needles.
That would be as not set dead on 28 degrees right????
Ok lets say just for argument sake that it is set spot on 28 degrees just like its supposed to be. At that point wouldnt you look at the carb????
thanks for the info Ralph