You need to pull your tank, on the left front, the two throttle cables runs into a black plastic housing almost under your bars. In that box is a cam and spring. Two cables run into the front of the cam, two cables runs back to the carbs and one runs down. Be careful of the spring and placement but pull it open and wipe any debris from the cables, lube them, inspect for proper placement and function and reassemble.
The cable running down is controlling the cruise, if you have different handle bars or the cam has been apart I would inspect to make sure they it is correctly in it's place. If you remove the throttle cables make sure they are in the correct location ( one is a pullback). Should be some threads on changing cables.
Follow your cable down and make sure it is connected at the other end.
http://venturerider.org/forum/showthread.php?t=71505&highlight=install+throttle+cables