Small Engines (Lawn Mowers, etc.): Kohler mod. CV15S typePS-526, starter fluid, gas filter

Question
I have a Craftsman tractor with the above Kohler engine. First my tractor started backfireing but could always get it going. Then it would quit running for no reason and very hard to get it going. Put new gas filter. Would turn over very well but would not start. Put all new saftey switches on. Did not help. Can pull the plug out and lay it on the engine shroud and turn it over and sometimes get spark but the spark looks weak.The plug is moist with gas.Sometimes after putting the plug back in it would start and run OK. Now it won't start for nothing. Still have a weak spark. Could the timing be messed up some way and if it is how do I correct this. I take very good care of this tractor and keep the maintanance up. If you could give me some advice I would sure appreciate it. I have run out of ideas. Thank you for your help.
Paul

Answer
 Hello Paul:

 Check the Oil. Do you Smell Gas? If yes, then Check the Gas Cap and Ensure it is Venting Properly. If it is, then  Clean and Overhaul the Carburator. **CHANGE THE OIL** Too Much Gas in the Cylinder will Allow for the Backfiring you were Getting. The Plug Should Not have Been Wet. Be Sure to Replace the Spark Plug and Set the Gap at .030. The Coil is Firing. A Coil will Either Fire or Not Fire. Some will Heat Up and Stop Firing. Go with the Carburator First. Stop the Flow of Gas to the Carburator and Try to Run the Engine on Starter Fluid for 25 to 30 Seconds. Will the Engine Run? If so, the the Carburator is the Cause of the Problem. Hope this Helps. Let me know what Happens, Please.

 Good Luck

 Respectfully

 John