Gasoline (petrol)

Extensive grass trimming was not common before the widespread application of the vertical shaft single cylinder gasoline/petrol engine. In the United States this development paralleled the market penetration of companies such as the Briggs & Stratton company of Wisconsin.

Most rotary push mowers are powered by internal combustion engines. Such engines are usually four-stroke engines, used for their greater torque and cleaner combustion (although a number of older models used two-stroke engines), running on gasoline (petrol) or other liquid fuels. Internal combustion engines used with lawn mowers normally have only one cylinder. Power generally ranges from four to seven horsepower. The engines usually have a carburetor and require a manual pull crank to start them, although an electric starter is offered on some models, particularly large riding and commercial mowers. Some mowers have a throttle control on the handlebar with which the operator can adjust the engine speed. Other mowers have a fixed, pre-set engine speed. All are equipped with a governor (often centrifugal/mechanical or air vane style) to open the throttle as needed to maintain the pre-selected speed when the force needed to cut the thicker or taller grass is encountered.Gasoline mowers have the advantages over electric mowers of greater power and distance range. They do create a significant amount of pollution due to the combustion in the engine, and their engines require periodic maintenance such as cleaning or replacement of the spark plug and air filter, and changing the engine oil.Growing awareness of the air pollution caused by small gas engines has resulted in some state-level legislation pushing consumers to chose machines with different power sources. October 9, 2021, California passed an air pollution control law AB1346 phasing out gasoline powered small off-road engines, like those found in lawn mowers, set to take effect January 1, 2024.

Electricity

Electric mowers are further subdivided into corded and cordless electric models. Both are relatively quiet, typically producing less than 75 decibels, while a gasoline lawn mower can be 95 decibels or more.

Corded electric mowers are limited in range by their trailing power cord, which may limit their use with lawns extending outward more than 100–150 feet (30–45 m) from the nearest available power outlet. There is the additional hazard with these machines of accidentally mowing over the power cable, which stops the mower and may put users at risk of receiving a dangerous electric shock. Installing a residual-current device (GFCI) on the outlet may reduce the shock risk.

Cordless electric mowers are powered by a variable number (typically 1–4) of 12-to-80-volt rechargeable batteries. Typically, more batteries mean more run time and/or power (and more weight). Batteries can be in the interior of the lawnmower or on the outside. If on the outside, the depleted batteries can be quickly swapped with recharged batteries. Cordless mowers have the maneuverability of a gasoline-powered mower and the environmental friendliness of a corded electric mower, but they are more expensive and come in fewer models (particularly the self-propelling type) than either. The eventual disposal of worn-out batteries is problematic (though some manufacturers offer to recycle them), and the motors in some cordless mowers tend to be less powerful than gasoline motors of the same total weight (including batteries).