An easier solution is to replace the fork springs with heavier ones, and changing the fork oil to a heavier weight.
http://faq.ninja250.org/wiki/How_do_..._suspension%3F
http://faq.ninja250.org/wiki/Which_t...ion_upgrade%3F
http://faq.ninja250.org/wiki/Front_suspension_upgrades
I've done the fork springs, I had an extra set from an EX500, so I cut them down, and then replaced the fork oil with 15wt, along with the rear shock from a ZX600 this set-up works for me.
http://faq.ninja250.org/wiki/Installing_a_ZX600_shock
IMHO upgrading the suspension on the Ninjette is the best upgrade one can do, and is a must do upgrade, and is the best bang for the buck.
Something else to consider is doing the fork seals and dust covers if there's any doubt about then. Nothing is more annoying than doing all that work, to only have them leak soon after, only to have to tear it apart again.
Finally is you have the extra cash laying around($180.00) get the Ricor INTIMINATOR
http://store.ricorshocks.com/product...20-1001nin.htm
Several members here have them and swear by them.
A Ninjette with the suspension dialed in, and a skilled rider will dominate the twisties .