throttle sticking KZ900 only when bike is running

Throttle only sticks when running, will return to idle with a little help and time but does not snap back by its self. I have lubed the cables adjusted so when bike is cold twist throttle and it snaps back. as soon as I start it it is a bit harder at start to twist and will stick to were I twist throttle and stay revving for a bit and returns slowly but not all the way to idle. Bike has sat for years worked fine for a bit then stated sticking after first couple of rides. Could it be thee return spring? or is the slides sticking in carb's, and should I take apart and clean. Bike idles great and great carb response when i twist it.

Put some slack in the accelerator cables. If that cures it, the cables are too tight or sticking. You can rule out cables by unhooking them from the carburetors and blip the throttle with the main linkage on the carb. If the problem still happens it's in the carbs.

Fix it where ever it is because you don't want a sticking throttle under any conditions.