I don't think going to 14:1 directly will be a smart thing to do. You might want to go to 11:1 or so. And if that works, gradually increase the compression. 6.4:1 is very low for an old 2-stroke, maybe your piston is worn out?
When you work the head, make sure you keep atleast 0.7 to 1mm squish (Room) between your piston and your head, to prevent the piston from hitting the head.
About the dual sparkplugs: Some people say they do work (keep the head cooler, burn cleaner) and some say it's BS. Try it for yourself.