Gravity needs to be a negative Y value if you want it to force down. By default gravity is at x:0 and Y:-50. I guess what @Christoph, @nayamamarshe and @heathclose meant by "increasing gravity force" is to actually decrease that number to -200 or -400. The gravity force is increased but the direction of the vector kept downwards... Also as @heathclose mentioned character Max Speed either should be 0 as "no limit" (yeah I know that's weird way to say infinite), or should be specified high enough so that max speed is fast enough for you but never faster than that. Oh and Air Drag also can alter your falling behavior of your character.
@nayamamarshe @heathclose @trudnai , Thank you so much for your answers.. the Air drag Did the trick, set the y attribute to -900.