Wait till the engines warmed up; and see if you can't adjust the flow; it may be running to rich. (its a screw on the carb.: top near back on a slight angle, see manual).
If that dont work:

I would advise against a rebuild due to cost; buy a new carb instead (149$) and keep your old one as a backup (since it sorta works). Rebuilt carbs for me have never worked so hot and it cost about 300 to pay someone to rebuilt it (though you could do this yourself, there is no guarentee your carb will run any better).

jon.