It sounds like you have a linkage bind and/or a butterfly that is not quite properly in place. It is very easy to get a bind in either spot. The butterfly can be loosened and then the throttle shaft forced to the full closed position (turn throttle stop scew all the way out so it doesn't get in the way) and re-tighten. If is is still a little sticky after that, removing the butterfly and chucking the throttle shaft in a drill and spinning it for a few seconds should hone the bush to the shaft very well. Then you remove the shft and clean very well and reassemble.
Sticky linkage can often be fixed by wiggling the carb on the base as you tighten the nuts so that the shaft is truely "in-line." Otherwise something may be bent or a pinch-bolted motion transfer arm is adjusted too close to the carby.
Mike!