How many miles on the scoot, have you removed the tupperware and checked the belt? Have you checked the final drive chain (sits in an oil bath on the left side of the scoot when you're behind it) There are factory spacers that need to be changed occasionally under the chain to keep proper tension. Sorry, just read again it has 18,000 miles, probably needs the drive belt; DON'T GET THE EBAY BELT!!!!! They will get you lots of practice replacing the belt, but the Mitsuboshi belt is OEM and handles the weight and torque much better. The J.Costa thread has some information on the belts and where to order them from, but pull some plastic and make sure the belt has failed, I think the maintenance interval is 20,000 miles, but if the previous owner only had two speeds (wide open and stopped) the belt could easily fail. There are good write ups about changing the belt and the special tools required, my challenge was the special lube the manuals want you to use, finally bought it from one of the guys on this forum. You do want to get the workshop manual, I both purchased a DVD and paid for a download, good to reference once you get to making repairs.