Justin : the only things that oculd make the carburetor stick are : dirt or lack of oil. It's possible your fuel may be bad.. sitting in the sun, or heat is bad for fuel. If thats not the case its possible something got in there. Take the carb apart, clean it and put it back together with a little after run oil or 3in1 oil.

If both of these are not the case, its possible the tension on your throttle return spring isnt set right. If you move the collet forward to increase the tension of your spring, it may help with closing the carb when you go back to neutral.