Sounds like you have a fuel jet plugged up. You can hear the motor pull in the air as the butterfly opens but there is just no fuel to burn........ Check for a weak spark. Maybe once the mix gets to strong you cant make the fire to burn it all.

Take off your air cleaner, with engine running, use some eye protection or a mirror look down the carb and open the throttle about half way. ( if stick shift be sure to block the wheels so it don't roll away on ya.! ) Look and see if your getting fuel down both barrels of the carb. If 4 BBL just look at the main barrels and jets. They should be pushing the same amount of fuel on both sides. If one is weak or no fuel then you have a plugged jet or some other carb problem.