A larger carb doesn't always mean more power. Lots of things to consider. The biggest thing is calibration. It's got to be right for the motor it's on or it won't make a difference at all, and can even lose power. I'd take that carb completely apart and blow out all the passages, make sure there's no debris in it at all. Put it back together and set the floats with the level at the bottom of the sight glasses to start, and see how it does from there. What jetting, air bleeds, etc are in the carb? Did you get it used or new?