What's the model of carb your using?
What happens when you drop the needle on clip?
What happens if you run the ATV without the air filter on?
Sounds to me you have too much air flowing to your motor,, it's bogging down your bike when accelerating, and when you let off the throttle it's still pulling gas because so much air is flowing through the carb.
You could try and make the inlet of the carb a bit smaller with a insert ring of some sort.
Timing advance might be an issue too, you'd have to know that your carb is tuned right first.