ok, got dyno jet stage 3 dialed in with K&N slip on filters and yoshi pipe. Time for plug change. Any recommendations? iridium, hotter or colder than stock? or stock? Yes, already way way quicker than stock. Changing plugs at 10,000 km. 1st change was stock plugs at 5000km. Plugs just tired and a little on dark side, but cant say if rich or lean cuz runs great, with a little pop on shut off now and then, theres racing plugs on amazon I am considering. Feedback guys./ gals, please

Try a colder plug to experiment.

If it looks that much carbon is depositing on it, go back to stock rate.

Check these:
http://www.dansmc.com/sparkplugs1.htm

http://faq.ninja250.org/wiki/Changing_the_spark_plugs_%26_brands_to_avoid

Never try a hotter one first !!!

I wouldn't change the heat range to a colder plug - especially if they are dark and you don't want to change the main jet.

If you were running at constant high RPMs for extended periods (LSR mostly, like Racer-X) or have increase the power significantly then go colder.

The stock plug heat range is a compromise, but so is most street riding.

Stick with a NGK in the stock range, but you could try a special type if you felt like experimenting. I wouldn't expect any significant gains though.

What main jet is in it? You may want to consider dropping a size because the plugs are dark.

Being that you are in the Philipines, you're not going to experience drastic temp extremes. Stick with the stock heat range NGK Iridium Spark Plugs (http://www.newninja.com/forums/f98/iridium-spark-plugs-8387.html) and you'll be fine. As far as the plug being dark, I wouldn't be too overly concerned, if the jet kit and slip on are the only engine mods you've done. "Dark plugs" look differently to different people. What may be a dark plug to you, may be considered normal by industry standards. Given that you've made your carb richer with larger jets, a slight bit off richness is expected. Knowing how to properly read a plug and what it should look like helps a lot in determining how you made need to tweak you engine.

Here is some good info that may offer a bit of help.

http://www.ninjette.org/forums/showthread.php?t=126960

Spark plug chart (http://www.ninjette.org/forums/null)
How to Read Your Spark Plug (http://www.4strokes.com/tech/sparkplg.asp)
FAQ Reading Spark Plugs (http://www.jetsrus.com/FAQs/FAQ_spark_plugs.htm)