How about help from a 250 weenie??
The coughing/backfiring/popping can be eliminated by doing the Kleen system removal.
http://www.ninjette.org/forums/showthread.php?t=9948
The coughing/backfiring/popping is due to the new can you put on. I had the same problem when I installed my Area P full system and removing the Kleen system solved it. Not a backfire or rumbling at low rpms cruising since.
If it is harder to take off from a stop, it is running lean and shimming sounds like it may help you. Getting to the carb slides is detailed here.
http://www.ninjette.org/forums/showthread.php?t=10736
Don't drill out the slides as Vex has done in that DIY... I was just using that as a good picture source on how to remove the slides.
Once you remove the slides, put 2 or 3 washers under the needles as explained in this thread...
http://www.kawiforums.com/showthread.php?t=105901
At the same time you shim, remove the intake snorkel.
http://www.ninjette.org/forums/showthread.php?t=10090
good luck... let us know if you need any help.
