Small Engines (Lawn Mowers, etc.): backfire/ afterfire, john deere 214, hp model

Question
Hi John,
Hope you had a Merry Christmas & a Happy New Year.
You help me in the past with a compression release problem,
so I come back to the expert.
I have a John Deere 214 lawn & garden Tractor.
Engine:Kohler 14 HP Model# K321AQS,Spec.# 60318.(1987).
It starts fine, but after a few minutes it starts to backfire/afterfire out of the muffler.It has new plug, points,carb overhaul,fuel filter,cleaned fuel tank,& system.It has been static timed.
It also has a new Kohler Coil.Which is the fourth one to be replaced.What am I doing wrong? Any & all help is greatly appreciated.
Thank You,
Bob  

Answer
Hello Bob:

Thanks. I had a Great Holiday Season and I Hope You and Yours did Also. 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 the Sectional File. Then Select the Section of the Mower you Wish to View Online. You can View a Breakdown of Just the Engine at this Site Addy; http://www.kohlerplus.com/login.asp and Select Enter as Guest. Now Select the Thumbnail of the Catalog you Wish to View. Have you Replaced the Condensor? Check the Point Set Contacts for Sticking/Burning. If the Contacts are Burnt/Sticking, then Replace the Point Set. You May have Purchased a Bad Point Set. How Often are you Replacing the Coils? Did you Soak the Carburetor when it was Cleaned? If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 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. Thanks.

Respectfully

John