Scooter won't accelerate?

Help,
My Vespa 150cc scooter will start and run, however, when you turn the handle to rev it up, it will not accelerate. The carburetor has been taken out and cleaned and new parts put in it, but that didn't do the job. Any ideas? I am trying to sell the scooter and this new problem just popped up the day a buyer was coming to look at it. Please let me know what you think, I would love to get it fixed and sold before fall.
Thanks

Its probably the cable from the hand grip to the carburetor. The guy that did your rebuild didn't fasten the cable securely to the carb. check that out. Reattach and there you go.

The exhaust system may be plugged. Remove the pipe and check for obstructions.

Could be a few things.... check the air filter... check the feul line to make sure it isnt restricted and the throttle cable.

It could be a throttle cable. I've read that well prepaired Vespa riders keep a spare cable and tire with them when they go for a ride. Since I don't know what year your Vespa is I'm not sure if you have a twist and go type CVT (gearbox/transimsion) or one with gears and a clutch. If you have a CVT then it may be possible that all you need is a kevlar belt replaced in your unit. I'm sure the Vespa ET2 and now ET4 50cc scooters have a CVT type unit and can last from 9K to 12k.