Sailing at the appropriate speed is very important, especially when participating in water sports or when there are swimmers or other boaters sharing the lake. For this reason, keeping your speedometer in good working order is crucial. In most cases, the speedometer works by implementing water and air pressure. As you sail, water is forced into a small hole either in the pitat pick-up or in the lower unit of the motor. The water forces the air in the tube to compress and moves the needle to show your speed. If the hole becomes clogged or damaged you will receive no reading or one that is inaccurate.
Check the tube in the back of the gauge and be sure it is not cut, kinked or tied too tightly for air to move through. If it is cut, you will need a replacement tube. Otherwise, untangle or loosen the wire or kinks and you should be ready to go.
Follow the tube to the back of the boat. Unscrew it out of the pitat pick-up or lower unit and attach it to an air compressor. Gently blow air through the tube. The needle on your gauge should move. If it doesn't, you will need to buy a new gauge.
Use the air compressor to dislodge debris from the tube by setting it to blow air with a little more pressure. If you cannot remove it, you can purchase a new tub and simply screw or insert it into your pitat pick up or lower unit.