Custom movement Acceleration by set speed?

can someone explain to me why I can't seem to use

custom movement set speed to accelerate?

the logic behind it would to use a code like

Set Player Speed to PlayerCustomMovementSpeed-40

I'm trying to do it this way so I can do something like

Set Player Speed to clamp(PlayerCustomMovementSpeed,-200,0)-40

and set my max speed through my movement instead of My overall speed

however it seems to just barely move the player upwards with no acceleration whatsoever

is this a bug? if so I can report it. if not how can I fix it?

Speed is a magnitude, so negative values probably won't work. You can see this with other behaviors such as the bullet behavior, as well.

hmm is there a way to do something like this with set speed to achieve a max acceleration?

preferably with the movement and not the overall max speed

bump I still need to know this