Timing problem

If it was a big vacuum leak, then the idle would be messed up too. It is more likely the progressive circuits, that cover the transition from idle to cruise; if it acts this way with a slow opening of the throttle, that is likely it. If with a fast opening of the throttle, then look at the accelerator pump, and the well under the nozzle; look for gum and crud around the check ball/weight in that well.

BTW, I really think you need to clean the carb thoroughly if you have not done so. Filters catch some things but not necessarily all of the super fine stuff. And they won't stop gum from forming in the carb after the ethanol has flowed through.