Home › Forum › Ask A Member › 1961 40hp Evinrude difficult to turn under compression › Reply To: 1961 40hp Evinrude difficult to turn under compression
Look at the outside of the cylinder h.ead, See those two lumps next to the spark plugs. Those two boxes, let’s call them, are closed containers, nothing inside them except air. Next to them you should see two valve stems with springs around them. When you pull the starter rope, the valves should be depressed. That adds the volume of air inside the “box” to the volume of air inside the compression chamber. Since the pistons are compressing a fixed amount of air into a larger total chamber volume, the pressure will be reduced (relieved somewhat). When the rope retracts, the valves close and normal compression returns. Bottom line, are the valves opening when you pull the rope?