I purchased a used Exmark Metro 36" (2003 model) in February 2006. It has a Kohler Command 15hp engine, pull start. The local Exmark dealer gave it a complete annual inspection (new gas, carb cleaning, new fuel lines, air/oil filters changed, etc.) and said it was in great condition. Even though I found this mower difficult to start, it ran fine all summer. Well, on Oct 1st, while mowing, the mower ran out of fuel. I refilled the tank and was unable to get the mower restarted. The fuel filter, which had previously been perfectly clean, had debris in it so I thought maybe I'd gummed up the fuel system. I replaced the fuel, fuel filter, checked fuel lines, checked float system in the carb. Engine still wouldn't start. I tried starter fluid in the carb--no start. Replaced spark plug. Still no start. Fuel is getting through to the spark plug so I think I have an ignition problem. I bypassed (jumped) the PTO and OPC safety switches and it still won't start. Now things get strange. One individual I spoke with suggested that the ignition coil might be the culprit. So before I dive into investigating the "magnets on the flywheel" I decide to check the spark plug one more time. I remove and replace the plug. The engine starts like a champ. I mow with it for two days and it works great. However, now it won't start again. Back to square one. Any ideas? I'm just a homeowner, not too technical. Could someone explain to me the numerous safety devices on this mower (Transmission, PTO switch, OPC switch, Engine Kill Terminal). Are the safeties to blame? Is it the Ignition Coil? How do I check these items? Could the gap on the plug be wrong? How important is the correct torque on the plug? Please help. Thank you!