You can get a bit more choke by gently bending down the tab circled in red seeings as your cable is already at the end of it's adjustment. This should solve your starting issue if you're not satisfied with how easy it starts. The more you restrict air flow on cold start up the easier it will start as manifold vacuum is forced to pull fuel up through the venturi to enable startup. With the choke not egaged all it does is suck air in from the filter housing.

As for your putt putt issues and dark exhaust emmisions 2 main things spring to mind from my experience. First and most likely is a blocked air filter, even though it may look clean and clear it's probably damp with oil and not letting it breathe. Remove the air filter from the assembly and start and run and see if this rectifies your problem. Second possible cause is a faulty spark plug, replace and check for symptoms.
There is a possible third cause, to do with the pilot jet, but this is unlikely given your symptoms and we'll get into that if the other 2 remedies fail to yeild favorable results.
Give these a try and report back and we'll go from there.
[Linked Image]