Tractor Repair: Craftsman Engine, oil fuel, exhaust pipe

Question
My engine just starting making this poping noise. Sounds almost like dropping water on a very hot exhaust pipe. It's got plenty of oil, the plug has not been changed in a while. Could be water in the tank maybe?  

Answer
Check the tune up -- it could be detonation or arching due to a bad plug wire -- missfire from water in fuel -- Start with the easy items - plug - wire - fuel.  Then check for any type of leaks - oil - fuel --- Rubber gasoline hoses can split and spray gasoline on hot exhaust parts -- that will cause a sizzling sound.


Thank you.

Eric