What is the manifold vacuum at light throttle cruise speed? The Carter carb has a mechanical metering rod that controls high speed mixture, not a vacuum operated power valve like a Rochester. It's possible the metering rod needs to be adjusted a little leaner for the best cruise mixture. Idle mixture can also be adjusted with a vacuum gauge. Turn the idle mixture screw clockwise until the vacuum begins to drop, then back it out until the vacuum peaks. Some people suggest going 1/8 turn richer on the idle screw after the vacuum maxes out to help the transition from idle to part throttle acceleration.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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