Craftsman Deck Lawn Tractor Review

The Sears store has a new line of cleaner-burning, fuel efficient, and a bit more power spark plugs. You might want to see what model new plug would be right for your tractor, to see if it makes a difference.
I'm assuming the fuel, oil and air filters have all been replaced on your unit.
That makes a powerful difference, too.
Mine runs rough, when I first turn it on at full-choke.
But, it calms down nicely, once it is set to the highest choke speed.
I try to stay away from "the turtle" on all of my machines.