Update function Problem...very odd

There is a problem I am having with this code. Basically it ramps up the speed of movement the farther you are in the level, but there is one problem...

 private var currentPosition : float;
 
 private var startTimer : float = 0;
 
 private var offset : float;
 
 private var scrollSpeed : float = 1;
 
 function Start () {    
     offset = 0;
     
     startTimer = 0;
 }
 
 function Update () {
     startTimer += 0.0175;
 
     offset = startTimer * scrollSpeed;
      
     if(offset >= 25 && offset < 40) {
             scrollSpeed=1.1;
     }
     else if(offset >= 40 && offset < 65) {
             scrollSpeed=1.2;
     }
     else if(offset >= 65 && offset < 95) {
             scrollSpeed=1.3;
     }
     else if(offset >= 95 && offset < 110){
             scrollSpeed=1.4;
     }
     else if(offset >= 110) {
             scrollSpeed=1.5;
     }
     
     print("sdfsdf: " + startTimer);
             
     var speed : float = scrollSpeed * 2;
     
     transform.position.z -= speed/6;
 }

(This code moves objects to the player at an increasing rate)

What goes wrong is that startTimer variable stops increasing about 2 seconds into the level. I have NO idea why it just stops.

However, when commenting out the line "transform.position.z -= speed/6", it increases just fine.

What am I doing wrong?