Briggs and Stratton 12.5 HP IC Veritical. Serial is 289707 0154 01. Engine won't crank unless spark plug is taken out. It is not an Overhead Valve. I guess it still works on the same prinicipal as a OHV engine. Would you take off the carb to get to the cover to see what the clearance is? I don't for the life of me know what to do next. Thanks.