those horses have a very low speed naturally, maybe thats affecting it?
Wait I think you were absolutely right!
The script multiplies the difference between minspeed and maxspeed with timepassed, and uses this value to up the speed -> this way holding the button for 1s means accelerating to full speed.
Now if the max speed is low, and/or the FPS is high, the speedmod value is between 0 and 1 - and apparently modactorvalue2 doesn′t accept decimal values!
I never noticed this before, cause I had so low FPS! Now I have better system, less mods installed and static 30FPS with Oblivion Stutter Remover -> the speedmod with these slow horses is always 0.76! :facepalm: