Hi I picked up this riding lawn mower used in poor condition. I repaired the carb and changed the oil. Carb had mineral deposits and a milky pink liquid at the bottom. Probably the mower was left outside for some time in rainy weather. There is rust in some areas. It ran very rough before, and now it runs smooth I guess with some rpm lowering every few seconds. I took the spark plug out and it was black. The entire inside of the combustions chamber is covered in what I think it carbon. Does anyone know what I should do from here ? I haven't tested any loads on the mower yet.