Are the gaskets in the carb good? Can you see or feel gas leaking anywhere around the carb? How's your air filter? Maybe the A/F ratio is set too rich.
As far as hard starts, your timing may be set too retarded or you have a vacuum leak (or both). Could be a choke issue too. Do you have an electric, manual or divorced choke?
I'm just throwing things out that have bit me in the past.