Every gasser carb ever made is designed with something to keep the disc in the middle...
The spring is to close the throttle on the chainsaws that most of them were made for...
If you take the spring completely out the disc will vibrate back and forth, cousing wear in 4 places where the disc meets the shaft at the ends, and the carb body itself on both ends of the shaft..When this happens the throttle can be completely closed and still not shut the engine off....There are a few Walbros with a slotted piece on the end of the throttle shaft, you could take the spring off these and the disc will still be in the center...The old WTA6 on G38s is one of these.....