Petrol lawn mowers come in both the 2 Stroke and 4 Stroke variety. 2 Stroke lawn mowers are more powerful, less expensive, have a better power to weight ratio, and can be operated in any orientation. However, they are also louder, less fuel efficient, and do not last as long due to the high revving engine. They also require the petrol to be mixed with oil prior to use in order to lubricate the engine.
4 Stoke lawn mowers by comparison are not as powerful, but contain an oil sump (a separate oil chamber) and don't need the fuel to be pre-mixed. This saves the operator from mixing the fuel but it also means that the mower cannot be tipped on one side as it will cause the oil to fall out of the sump into the fuel chamber.
