What is causing that aggravating sputtering sound from your lawn mower? Well, it depends on what kind of sound it is. If it is an intermittent sound and the lawn mower is losing power, you may very well have water in your gasoline.
Water in gas is a big problem today because of the ethanol that is added to it. Ethanol is essentially alcohol and alcohol attracts moisture from the air through an open vent cap or unsealed gas can.
When the engine is running, it will try to burn this water and will begin to sputter and especially under higher loads such as thicker grass. The sputtering may clear up or it may get worse. Alcohol is heavier than gasoline so it tends to sink to the bottom of the gas tank and the carburetor bowl. As the mower is cruising along, the water and gas will splash around and you may get some water sucked up into the carburetor or it may be a splash of gas.
What I like to do in this case is to shutoff the fuel and then pull the fuel line off the carburetor and get a fuel sample with a clear glass jar. If there is water in the gas tank, there will be water in the fuel system and that will need to be cleaned out.
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