Sounds like maybe you're not really on the idle circuit at idle. I'ld pull the carb and look carefully at the butterflies. The primary should be just about ready to expose the tiny transfer slot in the bore. Also make sure the secondaries are shut. I don't know about yours, but there's usually a stop screw in the baseplate that can hold the secondaries open. This is usually adjusted for big cams so you don't have to open the primary so far as to get into the transfer circuit. The transfer circuit handles the transition from idle to the main circuit, and if your on it the idle mixture adjust screws won't have much effect. Hope this makes sense.