Why won't my motorcycle's throttle close?

Last week I had to replace a broken speedometer cable on my motorcycle, involving a lot of dismantling. Since then, the throttle won't fully close and I found today that when I got up to about 30mph, I tried to close the throttle but it only went down a tiny bit. I've checked and the slide in the carburettor is moving freely, but as soon as it is started up it's revving too high and starts moving as soon as I engage the gear. The cable is in a slightly more awkward position than it was before, but it all seems fine. What do you think is causing it?