Small Engines (Lawn Mowers, etc.): STX38 John Deere, john deere stx38, john deere stx38 lawn tractor

Question
I have a John Deere STX38 lawn tractor, with a Kohler Command 13 engine with a black deck. Model # CV13S.
At the beginning of the mowing season, which was about a month ago, I replaced the spark plug, the fuel filter,  changed the oil & oil filter. The first 3-4 times I mowed this year, the mower ran fine. Then the last time I mowed, about half-way thru the cutting, the mower engine revs slowed down. The engine has continued to run slower than normal. It seemes like the engine is idling even though I have the throttle up as fast as it would go...Which is where I normally have the throttle when mowing. I have tried adjusting the carburetor but it did not help.    Any ideas as to what the problem might be?

Answer
Hello Mike:

>>You can View a Breakdown of the Engine at this Site Addy; http://www.kohlerplus.com/login.asp (IE5 or Higher Required) and Select Enter as Guest. Now Select the Thumbnail of the Engine Catalog you Wish to View.
>>You can View a Breakdown/IPL of the Engine and Mower at this Site Addy, http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.H... and Enter the Model Numbers and Click Find. Then Select your Model from the Search Results Area. Then Select the Sectional File. Then Select the Section of the Mower you Wish to View Online. *You can Drag the View Windows for Better Viewing.*
>>THINK SAFETY: Always Remove the Spark Plug Wire/s from the Spark Plug/s and Tie Away from the Spark before Working on Any Small Engine unless the Plug/s must be Connected to the Coil/s for Diagnostic Reasons.   
>>Have you Checked the Throttle Control Spring?
>>The Spring from the Throttle Control Bracket Pivot to the Governor Arm may have Broken or Jumped Off.
>>Does the Engine Idle Up above Normal Idle at All?
>>Is the Throttle Cable Moving the Throttle Bracket Pivot?
>>If you Hit a Snag or this Does Not Correct the Problem,  I Hope to be Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 5 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John