You probably want to use tween instead of lerp.
The final value in lerp is a percentage point between a and b. If a and b don't change and you use a fixed number for the lerp value, it's going to give you a fixed value in return.
Example: set position lerp(currentposition,targetposition,0.5) means halfway to the target position. The next tick it is run, go halfway again. Note the second time it is smaller, since you're closer. The amount will get less and less, and you never actually get to the target, only halfway closer each tick.
In your case, lerp(80, 98, 0.1) means 10% of the way from 80 to 98, which is 81.8. If nothing in the inputs change, it will always be 81.8.