Try fresh gas, after 3 months todays gas is pretty much garbage.
Run the suggested gas/oil ratio, it's what the carb is jetted for.
Extra oil will cause a lean condition less oil will cause it to run rich.
Need to keep it to that magic 14:1 fuel
air ratio, and OIL IS NOT FUEL
it doesn't burn (or shouldn't)
Rich and lean has nothing to do with oil content, it all has to do with fuel and the ideal fuel air ratio for a clean burn. (one of my biggest pet peeves is this misconception about rich and lean!)
If you are running 25:1 and you change to 50:1 all of a sudden you have twice the amount of gas and half the amount of oil being passed through the jet for the same volume of liquid, BUT you have the same volume of air.
NOW you have a rich condition because you have too much gas and not enough air in the fuel/air mixture.