Drained out 10+ year old oil from my 1981 Craftsman push mower with 3hp Briggs & Stratton. Refilled it with bulk 15w40 at my work. Then got the engine to run on gas poured in carb, would not run off gas in tank even after flushing it out. Took carb apart and cleaned it, after getting the mower running properly for a short period of time we drained it again and refilled with bulk 15w40.
I'm going to let it get used for a little more before draining a 3rd time and putting in Mobil 1 5w30.