Chevy 2,

I run the 8 port without a return spring.

However, when I ran the .21 Nitro Star, I just adjusted the throttle trim (transmitter) until the throtte opened all the way.

You can get it to go all the way open. It also helps to change steering servo to higher torque, then put the old steering servo on throttle. This give throttle faster and more torque for throttle and brakes too.

AdamB