Hello,
The first thing I would do is NOT use the FCK editor to change the text size, it creates lots of extra tags in the HTML and you will find that Google will index your page for the keyword of "font size" because there will be so many font size tags in the source code.
It is best to use a CSS class which you can assign to a p tag or div tag to size a section of text as you require. You add the code for the font size in your skin.CSS file.
It maybe worth having a look at this tutorial:
How to create resizable text