Small Engines (Lawn Mowers, etc.): Adjusting speed of JD 14sb, clutch disc, sectional view

Question
I have a 93 John Deere 14sb walk behind. I can no longer get it to move at the fastest walking speeds. I am thinking it runs at the 1,2 and 3 speeds and not at the 4 and 5 speeds. Have you an idea of what may be wrong and how to repair it?  

Answer
 Hello Lee:

 If the Belt is Not Stretched or Slipping, then the Clutch Disc inside the Transmission May need Replacing. You can View a Breakdown of this Mower at this Addy http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.H... and Enter the Model Number 14SB. Then Select your Mower. Then Select Sectional View. Then Select Transmission. Hope this Helps. Let me know what Happens, Please. I really like to know the Outcome. Thanks.

 Good Luck

 Respectfully

 John