While the carb is off,check your T-port sync; if the throttle is too far closed, the transfers will be as good as dead. You can still make it idle on the idle mixture screws, but when you gently apply the throttle, it takes a fraction of a second to bring the transfers up to speed, and that is often interpreted as a flat spot. Just crank in the curb idle screw 1 full turn and see if it gets better.