I guess you are using the Bar/Line View, and you should look under the Split menu, next to your split variable, and choose option 'Limit number of intervals to' and select the number.
(click on the word 'Auto intervals' for a list of options)

Thanks Paola -

I don't think I explained myself very well - I want to include all the data that is selected but when it is put into the bar/line view it doesn't fit on the screen (this is fine) and you would need to scroll, however when you scroll the axis disappears meaning there is no longer a scale on the graph - I've attached screen shots showing what I mean.

Is there a way to keep the y-axis in view even when I've scrolled to the right?

Thanks
Anna

Annna - Unfortunately, no, this has not yet been implemented but will be at some point. I have re-classified this as an Idea.

However....what you could try to do in the meantime is to enable the right hand Y axis to display the same scale. Even if you only have one series shown, you can select it twice in the Measures menu, then next to one of them choose left and next to other one right axis.
This way, during the horizontal scrolling, you will have either one or the other scale visible on the screen.
Another alternative is to use the value labels.