I have a Sears riding mower model 536.270282. It always ran fine. All of a sudden it was hard to start. Took several cranks. After half an hour of running it chocked and stopped. I found a mice nest on top of the engine. Cleaned it all out. Mower ran for 5 minutes then stopped and refused to start after that. It cranks but does not start. Changed spark plug. Nothing. Checked fuel on the other end of the filter, it flows fine. Could something have clogged the carburator? When it cranks, it is a dry crank. No smoke, no ignition. This could be no air getting to the ignition chamber. I did clean the air filter.