carb tuning.

check the easy stuff first. does your throttle at the handlebar/grip have a little pin that you have to seat in the handlebar by drilling a hole in the bar? i've had one like that and broke the pin off so it seemed like the throttle was working at the grip but wasn't really drawing the cable. before you take apart the carb which was most likely assembled properly try that...these kit throttles are notoriously cheap. sick bikes has a new throttle for about 20 bucks thats solid.

^^ This is why I recommend to just forget about the cheesy plastic peg in the throttle and replace it with a steel bolt. Works just as well and makes it much easier to remove the throttle.