It won't increase milage. And may marginally increase power elsewhere.
But you very well might see increase throttle response at tip in. Your effectively increasing the amount of air that can enter at a lesser throttle opening. People percieve this as it making more power.. but it's really not. It's no different than if you pushed the stock throttle open further. It's just artifically doing it for you.
If you want a cheap way of getting a small increase... knife edge the stock TB blade, shave off the screws, and thin down the blades rod.
He who is enslaved to the compass is free to sail the seas