Do you need a new decompression valve for your small engine? A decompression valve will reduce compression during start-up and allows you to pull the starter cord with less effort.If your decompression valve is not working you might have a hard time pulling the starter cord on your chainsaw, cut-off saw, or trimmer.eplacing a damaged or worn out decompression valve can avoid further damage. Jack's carries a wide range of decompression valves from the biggest manufacturers including, Dolmar, Husqvarna, Makita, Poulan, Redmax, Aftermarket-Stihl, and more.