I have a John Deere 115, Briggs engine. A couple days ago while mowing, it started sputtering and blowing black smoke. I parked it and shut it off. Now, it will not crank, just whirrs. Battery is good. Getting charge from solenoid to starter. Checked engine oil, smells like gas. Could this be the reason my engine will not crank? Wanting to try cleaning carb like Briggs recommends but want to know if engine done for before trying something that may be futile. Thanks.