I've been running my Exmark HP with 19 Kaw for three years without problem. All of a sudden, it won't start. I can spray carb cleaner in the carb and she'll run until I stop spraying. So far, I've replaced the fuel filter, fuel pump, ignition switch, float and pin. I've pulled and cleaned the carb, replaced all gaskets, everything looks good. But the stinkin thing still won't fire up. I'm a small operator who mows neighborhood lawns only, so I don't have a trailer to transport to the dealer, which is over an hour away anyway. Any suggestions as to what the problem could be?