? 20 hp intek plus not starting ?

I was mulching leaves when the motor starting straining then just stopped. I let is cool down as I thought the work was too much for it. I checked the gas prior to trying to restart it. The starter engages as it should and the motor turned over several times It sounded to me like maybe it wasn't getting spark. I took the plug out and cleaned. I tried again, same result...motor turned over but would not start.