The electrodes on a spark plug must be clean and sharp to produce the powerful spark required for ignition. The more worn or dirty a spark plug, the more attempts pulling the rope may be necessary in order to produce an adequate spark.
If you haven't tuned your engine recently and have to repeatedly pull on the rewind to start the engine, a damaged spark plug may be the culprit. Inconsistent firing, known as spark "miss," can result in sluggish engine operation and poor acceleration. A damaged spark plug may also cause excessive fuel consumption, deposits on the cylinder head and oil dilution.
Luckily, a spark plug is one of the easiest engine components to repair and an inexpensive one to replace. And your standard socket set may already include the most important tool - a spark plug socket.