This fall I was cleaning and synchronizing the carbs on a 99 Formula III 700. I had also disassembled and cleaned the clutches. I started it on a rev up stand and the dess feature would not let it rev up, so I pulled the tether and reinstalled it. The sled farted a little and continued to run so I could rev it up. As I revved it I could hear the secondary slapping open directly and thought I didn't get the spring in right. I walked to the other side of the shop with it idling, turned around and looked at the track, it appeared it was in reverse. I hit the kill switch while watching the engine coast to a stop, it was running in reverse. It ran ok, enough to open the raves, but if it was on the ground it wouldn't have moved due to the secondary thinking that it is not under load. I think with the proper secondary, any sled could be started, and run in reverse.