2008 Yamaha Raptor 250SE / 250SE2 Factory Service Manual, Page 276Get this manual
IGNITION SYSTEM EBS01034 EAS00745
4Ignition spark gap The following procedure applies to all of the spark plugs Disconnect the spark plug cap from the spark plug Connect the ignition checker and spark plug cap as shown Set the main switch to "ON" Measure the ignition spark gap Crank the engine by pushing the starter switch and gradually increase the spark gap until misfire occurs