I don't think you could ever over tighten those little allen screws enough to hurt that stainless steel cable. The allen screw would strip out before that happened. I cranked mine down as hard as I could get it so it wouldn't pull apart and haven't had any trouble in the year it's been on there. And I believe Rumble is right about the springs being a little close at the back. Plus I believe it puts less stress on the throttle linkage to install the small spring where you have both yours now and flip it around so the long end of the wire is towards the back then the other spring (the big one) should get hooked to the top of the carb linkage and run to a spring return mounted on the intake. I straightened out the tang on the linkage and drilled a little hole in it to hook the front spring. Doing it that way distributes the load on the throttle shaft more evenly. Also if you mount the throttle cable ball socket in the hole above the one you have it in it will make the pedal easier to push down because it's farther away from the center which increases leverage. It makes pedal travel a little more but it's easier on the throttle cable because of the increased leverage. One last thing to make sure of is to align the cable front to back with the throttle shaft so the cable isn't pulling sideways. Here's a couple pics of mine.
