Did you remove the main jet and spray tube and give them a good spray with carby cleaner and "stoke" the holes with a piece of bread tie wire,(a pick tool isn't small enough to get in there).
To assist in starting are you sure the throttle cable is fully closing the choke in the "start" position.
If it's not slowing down when you put it to "slow" it could be a couple of things:
1) are the linkages moving freely when everyting is assembled and the engine is off.
2) Ensure that the governor arm is tight and not slipping on the governor shaft.
3)try backing out the idle speed screw (it's the black plastic phillips head one in the front of the carby).
Try these simple suggestions, if you haven't already done so, and let us know how it goes
