First things first, check all fittings are secure and that all clips are in the correct position and tight, make sure the airbox rubbers are fully seated as they have a tendancy to nip in at the lower edge on the inner two carbs which is damned hard to see.
Check the throttle return cable is not tight, surprisingly enough if it's a little tight it will make the engine hang like it does on yours.
Check your carb synchronisation, you'll need some balancer guages, very easy job.
Usual rule of fault diagnosis, always go to the last thing you touched, in your case the carbs.
