I just bought a Craftsman snowblower model 247.889720 with the 208 cc "quiet" motor. I had a similar problem--uneven running with the choke supposedly open. I found that the dial for the choke has confusing markings. Straight up and down is usually a full open choke. In this case, a full right turn is a closed choke, up and down is half choke, and all the way to the left is the open-choke, running position. Very unusual. At first, from the markings, I thought left and right turns closed the choke. It was functioning but not running smoothly in the up and down position, could smell lots of unburned gas and the fuel consumption seemed very high. On this model there appears to be no air filter and it would take a lot of disassembly to actually see the choke blade in the carburetor. I decided to experiment with the full left position and that cured the problem--smooth running and no smell of unburned gas from an over-rich mix due to the choke being half closed..