Regarding bike not spooling up; check the airbox for rodent nest, or other debris... ( yes, I know it's NEW, still, check it. ) Next, remove 4 screws retaining carburetor float bowl, ascertain cleanliness, and check for free motion of float needle. check for kinked fuel line from petcock to carb, you may have pinched the line when changing fuel tank. Also, slight possibility that new O/S tank had a particle or two which is now restricting fuel flow... Thats my 3 guesses. Let me know what I win.