trx300fw carb issues

Hello,
I recently rebuilt the top end on a 1988 trx300fw and am now having idle issues. Some times the ATV will idle slow so I idle it up. It will idle normally for awhile then after about 5 minutes of riding it will idle very fast. I installed a plug in the starter jet hole as the manual said to do. Is that a special type of plug? What could I try doing to get a normal idle?
Thanks
JStok