how did you test for spark? A plug can fire outside a cylinder but with compression fail. Were it me, I would buy a new fresh plug from a known good source and not Amazon. Then blow the cylinder out with compressed air to make sure it is not flooded. Pull it over a few times with the plug out, blow it out again THEN put a TINY amount of new gasoline in it thru the plug hole, put the new plug in gapped properly and see if it fires once or twice. Also, a plug can have spark when it screwed in but the center electrode be shorted to ground by carbon etc..