RE: carb does not return all the way
Reset your stop collars. Don't use a spring with the redcat servo it will wear out the hole where the servo horn shaft sticks out. I would reset my stop collars and fix it the right way though. The spring on the throttle rod is there to push throttle back. If your throttle is not closing all the way, either you stop collars are out of place, the servo is going bad OR the trim on the transmitter is turned up to far.
Also I agree with tylerjackson about the servos.