My 10 year old riding mower has an Intek engine model 31P777. Lately, I noticed that when I make a quick turn or sudden stop, the engine spews a puff of smoke that smells like burning oil. I always keep the oil level btw Min and Max. I do change oil and filter every season. Is this a sign of aging, or there is something wrong with it? By the way, this is not a commercial mower and I run no more than 30 hours a year.