Engine cranks but will not start. Good spark to spark plug. Eventually the battery wore down from cranking so I jumped it from auto. Still no start. Then I started auto and lawn tractor fired right up. Then I shut the tractor and the auto off and tried restarting. No start. Put jumper cables back on, still no start. Then I restarted auto and tractor again fired right up. Seems it won't start with 12 volts but will with 14 volts.