Small Engines (Lawn Mowers, etc.): 116 John Deere, engine model type, john deere lawn tractor

Question
Hello, I have a 116 John Deere lawn tractor that I have just bought used. When I first bought it, it would start no problem and run good. Then I had trouble starting it, so I checked the battery and there was no problem with it. I discovered that the starter was no good, so I replaced that and the spark plugs. Then it ran good. Now I am having the same problem again. It will turn over but not start. Can you please help me. I am confused.

Answer
What engine is on the mower?  What is the engine model, type and code/serial number?  

Get some new plugs and replace again.  I know it seems odd but we have problems with some spark plugs in some engines.  What brand of spark plugs are you using?

Let me know the engine and spark plug info.

Eric