Hi, guys need some help. I have a Craftsman Lawn tractor with a Kohler Pro 17hp OHV engine in it. When I start it, it locks up after turning the key a few more times it finally starts,but it blows gas out of the exhaust. Now I notice I have gas in my oil.What do you guys think it is, and do I have something major going on here and I should bring it to a repair shop,Thanks in advance.Bob