Add another reason to my list of why I hate wintertime. My 728 Simplicity has set outside, covered up. I decided to uncover and start it yesterday. It and ran great when I parked it , but would not start now. It had spark and all seemed well with the fuel system. Holding my hand over the end of the muffler , I can feel some pull as well as push. Obviously the exhaust valve is not sealing properly. I'll deal with it over the next few days.