Petrol engines are either two or four stroke and this refers to the number of revolutions the engine goes through to complete a single power stroke. There are pros and cons to each type of engine and you’ll normally find details about your engine on the product listing or packaging. However, if you do not have access to this, you can tell the difference by looking at the fill ports for the engine. If yours has a single port where you can add both oil and petrol, then this is a two-stroke engine. If there are two ports; one for petrol and one for oil then this will be a four stroke engine. It is essential that you NEVER mix oil and petrol in these types of four-stroke engines.