In addition, the Gyro has a ball-bearing built into it, so it has very little friction while turning.
Every part in a brake system has a certain amount of "travel" available. For instance, the lever can go from its rest position (which is often adjustable for hand size by a small screw) as you squeeze it to the point where the lever bumps into the handlebar grip.
The caliper has a limited amount of travel too, limited by the brake shoes hitting the rim on the inward side, and by whatever stops the arms from springing out when the brake is released.
On any braking system, the outward (rest position) travel should be limited by the lever's bumping against its stop, but the inward travel should be limited only by the brake shoes' hitting the rim. You should be able to squeeze the lever as hard as you can without having the lever bump into the grip, because once the lever bottoms out, no more braking power is transmitted to the brake shoes, no matter how much harder you squeeze.
The Gyro has a limited amount of travel available to it also, and it is important to ensure that the Gyro itself is not the limiting factor in either inward or outward travel.
Start by hooking up the upper cable between the lever and the Gyro. Operate the lever with one hand while pulling downward on the Gyro assembly. The adjusting barrels on the Gyro (and on the lever, if there is one) should be set so that the lever just barely stops the Gyro from bottoming out against the headset when you release the lever.
Make sure that the adjusting barrels on both sides are set the same way, so that the Gyro is horizontal. Otherwise, the braking action may vary as you turn the handlebars.
Once the upper cable is set, connect the lower cable to the brake in the usual manner.