Yep I had the problem on my Fuel EX 9. Try this.
Loosen up the stem enough so that the fork can move freely. Now tighten the screw thats on top of the headset just a bit. Check to see if its better. If its still loose repeat again. Dont keep torquen the screw in untill its tight because its not supposed to get tight. Just give it a little turn at a time. Heres a link video:
http://www.artscyclery.com/learningvideos.html?ccode=MTBMNTNCE&video=HEADSETM
Hope this helps
Loosen up the stem enough so that the fork can move freely. Now tighten the screw thats on top of the headset just a bit. Check to see if its better. If its still loose repeat again. Dont keep torquen the screw in untill its tight because its not supposed to get tight. Just give it a little turn at a time. Heres a link video:
http://www.artscyclery.com/learningvideos.html?ccode=MTBMNTNCE&video=HEADSETM
Hope this helps