Hey I just looked at what you were saying " still idles HIGH"... this is a correction to my earlier response. You may want to first apply carb sealant to eliminate any possible air leaks both on the carb as well as the back plate. However, it almost sounds like your engine may be dirty on inside. I know you said this was a new engine. It may have shavings inside that you need to clean. Since it is new I doubt that you have a piston/sleeve compression issue. Just make sure when you finish running your RC you always turn your flywheel to get your Piston at BDC(bottom dead center) so that you do not stretch your sleeve and loose your compression. Really sounds like an air leak though but I would probably break the engine down and clean it with denatured alcohol and relubricate the internals to be on the safe side.