Hi,Brewster! If you go to Fred's Guide you can't go wrong.But to save a little time,check your points for corrosion or pitting or wrong adjustment.That or a bad spark plug wire will weaken your spark along with corroded magnets.But just turning your flywheel by hand and not kicking it over will not usually show you the full strength of your spark.AND ALWAYS REPLACE THE SPARK PLUG.It can't hurt to have a spare.Are you sure that's the right number plug? Check it out before you buy a new one.Be sure to peruse Fred's Guide anyway.That way you won't miss anything! BYE!