To know if your lawnmower is a 2 or 4-stroke, you will need to check the engine type. Most lawnmowers have their engine type printed on the engine itself. If it doesn't say, you can always consult your owner's manual. If your lawnmower has a 2-stroke engine, it means that the engine fires once every revolution of the crankshaft. A 4-stroke engine, on the other hand, fires once every other revolution of the crankshaft. Generally speaking, 4-stroke engines are more powerful and efficient than 2-stroke engines. They also tend to be quieter and produce less emissions. However, they may require more maintenance than a 2-stroke engine. If you're not sure which type of engine your lawnmower has, it's always best to consult your owner's manual or a qualified technician.