I've got a Sachs moped that won't rev up or drive without holding the choke in like at least half-way. It idles excellent without the choke, but when you open the throttle it just dies. Ive cleaned the carb, and points. Ive taken off the exhuast and it makes no difference. This bike only has 180miles so I didn't think it was a carbon buildup anyway. What do you think is the problem here?