Did you loosen the clamps on the throttle shaft link between the carb? -- 1/4 inch box end wrench or socket needed. The mixture and idle speed must be adjusted on each carb independently and then when the clamps are tightened you have to check to make sure the carbs are operating in unison--a quick blip on the throttle should lift the pistons together.
Also check that the needles are properly seated in the pistons. You'd have to remove them but you could also check that the throttle plates are secure and closing properly. -- Dave