Jett is probably the best. If that is too much then the next best is probably the Fox .60. You can get it for half off if you trade in an old clunker; even an old broken, unrepairable 1/2 A engine. Be sure to get the new twin needle carb, said to be the best yet.
http://jettengineering.com/
http://www.foxmanufacturing.com/inde...roducts_id=287
Be sure to click on the image of the carb below.
http://www.foxmanufacturing.com/inde...oducts_id=1514
Note that both manufactures are still around, and both give excellent service for parts and repair.