In fact, there was a rule that enforced a mechanical carb closing device for just in the case you got a blackout on your receiver pack (is that rule still in the rulebook?) besides a failsafe, NOTHING than a return spring or a rubber band can close your carb if you run out of juice and avoids rundowns and full throttle smashess to the nearest concrete wall (don't know why, but a car without Rx battery, loves them. )