I am confused
Why is the spring keeping
it from closing?
Are you sure it's not the idle screw that is keeping the throttle plate open?
Normally the spring just pulls the plate closed to overcome the cable resistance etc
take off the cable and spring and use your hand to close the throttle, look down into carb,is plate closed all the way?
If not look for the idle screw, it will be touching the linkage at some point,this may be the issue with plate not closing
--to idle; air must be allowed to "leak" around the plate,idle airscrews and holes in throttle plates and other passages (dependant on carb...this is very general example) do this as well as idle screws slightly holding plate open
The spring mounted should be at angle that will not
allow the spring to be extended and "wrap" or touch the throttle shaft at WOT
A pic of your setup would help