About every 20 lawns or so, when i go to start the my mower, I get one small puff of smoke. I can't quite tell if it's oil or if it's gas. The mower has never done it on the first start up of the day. Here's the mower... Exmark LazHP 52" 23 KAW Kaw Syn Oil 255 hours I notice I burn about 1/4 quart of oil between changes. Should I be worried?