Remove the 500. In theory the more gravity you have the higher the speed you jump with to achieve a static height.
If gravity is 800 you jump with the speed of 800 * x. If your gravity is 100 then youll jump with a vertical velocity of 100 * x.
x here is a small number you can change (but 500 is too big). In theory this should work.
Try removing the multiplication by 500 for now.