STARTING PROBLEMS MAY BE CAUSED BY SOME PEOPLE USING SPARK PLUGS THAT HAVE BUILT IN RESISTORS IN THEM. THIS COMBINED WITH EITHER SPARK PLUG LEADS OR CAPS THAT HAVE BUILT IN RESISTORS WILL SUPPRESS SPARK WHEN SCREWED BACK INTO HEAD. YES I KNOW IT SEEMS THAT THEY ARE SPARKING WHEN YOU HAVE THEM OUT OF THE HEAD BUT IT DOES NOT OCCUR UNTIL YOU SCREW THEM BACK INTO HEAD AND THEN WHEN YOU CRANK THE ENGINE OVER AND OVER AND OVER AND OVER AND OVER AND OVER THAT THE SPARK PLUGS ARE NOT SPARKING CORRECTLY. USE SPARK PLUGS NGK BP 7ES.