My brother has a craftsman riding mower with a 16 hsp. B&S engine that ran great all summer.now he just pulled it out to cut the grass and it won't start.It turns over fine, gets plenty of gas, and tried starting fluid. Don't think it is a fuel issue.Checked for spark and looked pretty good,thinking maybe not enough there to fire the engine. He did replace the spark plug.CAN ANYONE HELP!!