Dude,
Make sure that she can take full throttle up to redline without a hiccup or hesitation. Any hesitation or "out of steam" feeling requires an increase of main jet. Go a step at a time. One step is significant.
After that, cruise on a flat surface in 3rd or 4th at mid RPM and listen (head to tank so you can hear the engine) on whether she's got a slight miss. If so, add a shim. Make darn sure that the shims are the same thickness. I use the Radio Shack ones and they vary. Slide a bunch down a nail and pick the ones that are closest (I don't have a mic). Add one at a time until the problem goes away. Adding too many drops MPG by a bunch.
This is a good shadetree approach to non-dyno jetting that's worked well for me since the original 2" mod. Since then, the K&N and full header have exercised it well. Anyone that focuses on adding shims instead of selecting a correct main is wasting fyuel and power.
As for the plugs, my cross reference from hell says that the CR9EK crosses with 4302 Autolite, X27EPR-U9 Nippondenso, R121XLS AC Delco, XR4CS Bosch, and RA6HC Champion.
Marc/Atlanta