Here is the msdn info for the Chart Axis
Axis[
^]
Then set
chart1.ChartAreas["ChartArea1"].AxisY.Minimum = 80;
chart1.ChartAreas["ChartArea1"].AxisY.Maximum = 90;
This can also be done right from the properties window -> ChartAreas->Axes->Y (Value) Axis->Minimum / Maximum
There are sooo many other properties that can be manipulated too.
And technically the IsStartedFromZero does not have to be false for this to work..