I would try adjusting the cable at the top of the carb completely one way then completely the other if nothing changes then I would think you might have a cable problem. remove the cable end from the throttle handle on the bars to see if that helps if it does then you are probably right the cable could be too short.

__________________
visit my blog for Riding in the hood,... The home brew bike journal....http://frictiondrivebicycles.blogspot.com/ The deacon's fiction