...i'm not sure that you should adjust anything, but trace the cable back and find out what's pulling it....
..see, the black sheath is only there for protection of the steel cable...
..somewhere, something is drastically pulling on that sheath...
..has to be fairly drastic for it to make the steel cable actuate the carburetor's throttle....
..if you don't find it, it could wear through the sheath, and allow moisture and grit inside, which might cause your steel cable to rust, hang-up and maybe eventually break...