There are a couple of things to check. First, check the tire pressure and make sure that it is between 17 and 20 pounds of pressure. Second, make sure that the skid plate (this is the plate that the tire pushes the ball against to throw it) is set low enough that the tire gets a good pinch on the ball. The space between the tire and the skid plate should be one quarter to one half inch smaller than the balls you are using. Third, try scuffing the tire with some fine grade sandpaper. New tires sometimes have what we call a "shine" on them (it almost looks like a varnish). A tire with a little wear on it pitches better than a new out of the box.