You need to isolate your problem. Is it the throttle grip, the cable(s), or the carburetor? I don't know that particular bike, but you can usually disconnect the cable where it connects to the carburetor. If it has only a single throttle cable, you can usually move the carburetor part and allow the cable to flex. Anyway, the idea is to find out what moves and what doesn't, then fix the part that doesn't.