flooding and backfiring on stop with Walbro LMK carb?

My lawn tractor (with Koler 18 hp engine) has a Walbro LMK carburator. It is flooding and will backfire when the engine is turned off. new airfilter, fuelfilter, fresh fuel, new sparkplug. in the winter it requires carb cleaner just to get it to start to use the snow thrower. In the cold it runs very rough until warmed up but even then isn't right.

how do i fix this?