Welcome to the world of midrange maladies and gas engines. I'm breaking mine in on a 26x10 and petroleum based oil and it's fine so far. What are you using and how many gallons of fuel has the engine seen? If spank brand new, give it a couple of gallons to settle in. If it's still rich in the mid range, try one of the carb fixes listed in the 3W literature, or search on the board for them. Basically you can add a vent tube leading to the venturi, a vent tube leading into the fuse, a carb shield, or the 3W horn. I've settled into the horn on mine and it's perfect. Takes a little fiddling, but it can be worked out with some patience. Let me know how you make out_bob