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What is a Lawn Mower Carburetor?

By Lori Kilchermann
Updated May 16, 2024
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A lawn mower carburetor is a device found on gasoline-powered lawn mower engines. The flow of fuel to the engine is controlled by the lawn mower carburetor. Unlike the system used on an automobile, the carburetor on a lawn mower is typically mounted in a horizontal manner and contains no throttle butterflies. With a rubber-type push bulb on the side of the carburetor, fuel is primed into the unit by depressing the bulb several times on a push-type lawn mower. After the carburetor has been sufficiently primed, the engine can be pulled over with the pull rope and started.

The throttle on a lawn mower carburetor typically has three settings from slow to fast, as well as a choke position for cold weather starting. As the throttle lever is pushed from slow to fast, the flow of air is increased and the engine begins to operate at a higher rate of speed or revolutions per minute (RPM) as more fuel is drawn into the carburetor. An internal combustion engine is nothing more than an air pump; the amount of air allowed to flow into an engine will dictate the amount of power the engine is capable of producing.

The biggest enemy of the lawn mower carburetor is old gasoline. Leaving old gasoline in a lawn mower's gas tank over the off season is a surefire recipe for creating a rough-running lawn mower engine in the spring that is difficult to start. Old gasoline creates what is known as shellac in the fuel system. This shellac gums up the inner workings and air and fuel jets within the carburetor, which blocks fuel and air from passing through them. The only remedy for a gummed-up carburetor is a thorough cleaning, which includes removing the carburetor and using a quality carburetor cleaner to diminish the offending shellac.

While not recognized as the leading cause of damage, dirt is a definite enemy of any lawn mower carburetor. Maintaining a clean and operable air cleaner on a mower will prevent most dirt and debris from entering the carburetor. Typically manufactured of foam with a coating of oil, the lawn mower air filter is easy to clean and maintain. After removing the air filter cover via the single screw with a flat-bladed screwdriver, the foam filter can be washed clean with hot soapy water. A quality dish detergent will cut the grease and dirt with ease.

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Discussion Comments
By Melonlity — On May 20, 2014

Old gas is bad for carburetors and so is gas with ethanol in it. Unfortunately, fuel with ethanol in it is common and few people realize how bad it is for a lawn mower engine.

Fortunately, a dealer must disclose if they sell gas with ethanol in it. Avoid that fuel and find some that is not cut with ethanol. There are quite a few gas stations that still use "pure" gas and they tend to brag about it. That pure fuel will cost a bit more per gallon than gas with ethanol in it, but it is worth it if that gas will extend the life of your mower, right?

By Soulfox — On May 19, 2014

It is not uncommon to find that shellac buildup in lawnmowers because people do tend to run old gas in them. How many people think to drain their gas tanks completely after mowing season has ended? How many people use old gas that's been sitting around in a fuel can all winter when it is time to mow again?

One thing that might help remove that without going into too much repair is good, old fashioned carburetor cleaner that people routinely use in their cars. A carburetor in a lawn mower isn't that much different from one used in a car, after all, and the same "pour in" methods used to keep automotive fuel systems clean will often work well with lawn mowers.

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