I thought this might be interesting.
The YFZ's stock thumb throttle cable controls the high performance FCR carb,(as opposed to the vacuum type carb that comes stock on the Honda TRX450R, which uses a slower intake vacuum to control the slide position. Comparatively, this gives Yamaha's FCR carb a much faster throttle response rate).
The YFZ's stock thumb throttle assembly is controlled with a single throttle cable that directly controls the up and down movement of the throttle slide. According to Yamaha one of the challenges of utilizing this high performance carb was the safety factor in case of a stuck throttle situation. The YZ twist throttle combats this potential problem by having a separate throttle cable that pulls the slide back down when the twist throttle is turned back to neutral. On the YFZ, which as you know uses a thumb throttle, there is no way to utilize a secondary throttle cable. With that said, the stock YFZ uses an electronic version of Yamaha's patented T.O.R.S. (Throttle Override System). This system monitors both the thumb throttle and carb slide positions. As long as they are in sync everything is great. However, if by chance you let off the throttle and the slide stays open, the system shuts down the engine automatically to prevent a stuck throttle situation.
The above explanation is why you don't want to mess with the stock thumb throttle system unless you prefer to switch to a twist throttle. If so, you will be disabling the TORS system and should run Yamaha's dual throttle cable system found on the YZ450F. By all means, don't run a single twist aftermarket throttle cable! Yamaha's double cable system is added safety insurance that you don't want to go without anytime you ride. Take advantage of Yamaha's safety advancements and install the Yamaha stock YZ assembly and cable -- if not for your own safety do it for the safety of others on the track with you! To install the YZ cable properly, you'll need to drill and tap the secondary hole on the YFZ's throttle body to allow the ability to use the push-pull YZ cable.