Mr Ziffel wrote:I've had my cub for about two years now and it runs to my satisfaction
If it is running to your satisfaction I would highly suggest leaving it alone. Don't open a can of worms needlessly.
While your diagnosis is probably correct, as the previous poster stated there isn't much to adjust. Unless you spend a considerable amount of time at curb idle, the idle mixture screw is not going to cause excessive carbon.
I have 2 cubs that fire almost immediately without choke. When it gets really cold, the choke has to be feathered to keep them running once started until it warms up. I encourage people to start cranking before choking to prevent hard starting due to an over rich fuel / air mixture as well as flooding.
If you do have a mechanical issue, look for it to be at the choke rod where it attaches to the butterfly assembly. Pull the hose to the air cleaner and determine that the choke is fully open when the choke rod is pushed in. If it is partially closed with the rod pushed in, you have determined why it starts easily and tends to carbon the plugs. Adjust the choke shaft as necessary.