A return spring is a good idea to save your engine because the link will usually pop off in a crash. Fail safe or any radio input won't help you there.
I can't see the head staying together at full throttle with no pitch and I wouldn't want to be anywhere around it while trying to bring it in!
It needs to be a light and linear coil spring around the throttle shaft like most autos have, not a screen-door tension spring pulling on the arm.
I got some springs from an old junked VCR that should work but have yet to get them rigged up.

Kirk