forget the old oil .i use maxima 927 castor oil 32.1 in all my lawn boys .its exspensive but good stuff. My motorcycle mechanic highly recommends it in all 2 stroke engines.Some one on this site said that it is only for high rpm engines but i beg to differ.it burns real well and ever since i have used it my mower doesnt smoke as much and the little black goop around muffler is gone.i have 5 lawn boys , 2 echo blowers and a echo trimmer , a cr250r honda and they all run great on this oil.it smells great too.i run the 93 octane in everything and have for years with absolutely no problems.