I agree that the transmission throttle linkage is likely the source of your cable sticking plus it is setup wrong. The bolt and washer that are holding the slotted link to the carb linkage look to be at a slight angle and binding. As mentioned, this should be a smooth stud and the link should be adjusted so the back part of the slot is right up at the stud, not the forward part of the slot. The idea of the long slot is that if the transmission linkage were to bind and not return for some reason, the slot would allow the throttle to return to idle. Besides, with the way it is set now, it is not operating the transmission linkage properly either.