Things to check:
1. Throttle cable -- this is a probability, IMO, based on your description. Make sure it's not getting hung up. It must fully return when you let go of the throttle.
2. make sure you have *no* vacuum leaks around the intake.
Did you replace the o-rings? Did you fully clean the carbs? and if so, did you make sure everything was properly adjusted and returned to stock (I assume) settings?
A