Clean the carb and slides with carb cleaner. If you lube the slides, lube them with two stroke oil. As soon as premix gas gets in there they'll get lubed anyways so it won't hurt to lube them.
If you have TORS, be sure that the short throttle cables inside the TORS housings are not bent. (this one got me before)
Replace the throttle cable. Sometimes the throttle cable frays inside the tube. Also, lube the throttle cable with good cable lube. Make sure it's not kinked or in a bind when putting it back on.
Remove the throttle cover and make sure it's clean in there as well.
That should eliminate every issuer possible with a sticky throttle.