Re: C02 tank/air tank questions for build
The kill switch can work the same way as on the gas engine. Short the coil output or ground it, no voltage potential is felt on the solenoid. With the air solenoid shut, the engine quits. The biggest hurdle I think will be throttle. You'll find that a ball valve is terrible at throttling flow, but still easier to control on a bike than a globe valve (like a water spigot).
Never stop wrenching