Are you letting it warm up at all before riding? Mine's very cold natured, and doesn't like to GO until it's started to get hot. Giving it too much throttle at low RPM before the engine is warm will yield hesitation, and even stalling depending on the circumstances. Mine's always done it. I let it warm up in the mornings for a couple of minutes, and keep it above 3-4000 RPMs during acceleration. Mine starts better without the choke when it's hot outside, or parked in a hot garage, but it does idle low, requiring some throttle input for a few seconds after starting. It only likes the choke when it's cold outside.
If none of this works, or it continues to run badly after it's warmed up, it's likely that stale gas has clogged the jets in the carb from sitting in the dealership. They're really not supposed to put gas in them for this reason. You might want to unhook the gas line, turn the petcock to "prime" and drain the gas out of the tank, and re-fill with fresh. Also dump 1/2 to 3/4 can of Seafoam in a full tank and run it until it's empty. This will aid in clearing out the carbs.
Good luck and keep us posted.