Small Engines (Lawn Mowers, etc.): 6 HP Briggs and Stratton Tiller engine, briggs and stratton, internal passages

Question
When under load, engine rpms start oscillating and abruptly stop with a back fire. It happens within 5 minutes of operation. I have cleaned carbuerator. It had water in it. What can be causing these oscillations and subsequent shut down?  

Answer
This oscillation indicates there is a lack of fuel to supply the engine under load and the cycle of the engine revving up (by the governor) and dying down (due to lack of fuel) is the result.  If the carburetor has a high speed mixture adjustment screw, start with an initial setting of 1 1/2 turns out from lightly seated.  If this setting doesn't correct the problem, continue to open the screw 1/8 of a turn at a time.  If this adjustment has no effect, the carb will need to be cleaned again.  This includes pushing a piece of tag wire through all of the internal passages and follow with carb cleaner.  Hope this helps.