I just had my new Bobcat 36" at the shop because it was blowing oil out the exhaust and smoking like crazy. I assumed bad rings or pass valve. The shop owner told me it was caused by dirty gas clogging the carb and filling into the oil. This is apparently happening all over the place, with the price of gas going up the quality is going down even at reputable gas stations. The shop owner recommend that I begin filtering my gas. Just another thing to watch.