Get a Fox .60 or .74. Improved carb. Won the MA.60 shootoff back in 2000 or so. Runs great on cheaper low nitro fuel. You can get it for half price if you turn in a junker, even an old busted 1/2A engine. The only thing better would be a Jett.
http://www.foxmanufacturing.com/inde...roducts_id=289
http://www.foxmanufacturing.com/inde...ge&pID=279
http://www.foxmanufacturing.com/inde...e&pID=1514