Sticking carb needle and seat comes to mind.
NEVER over fill the oil. Keep it exactly at the full mark only. Check oil prior to every mow. There is a reason they put the full mark where it is. Most engines the crankshaft gets into the oil and causes foaming which are air molecules inside the oil. Air doesn't lubricate very well. See where this is going? On engines with oil pumps, causes more issues like cavitation.
slomo