I have a Exmark metro with a 15hp Kohler. Today I (easily) started it and walked it to the garage so I could put new mulching blades on. I placed the front casters on a cooler and changed the blades. After I set it down it would not start and the cord was hard to pull. I checked the spark plug and it was fouled. I replaced it and still it will not start. When the spark plug is out the cord pulls fine. Sorry I am not mechanically inclined, so any suggestions would be great!