If they are airguide style, they are a simple pitot tube system. There will be a tube going into the rear of the speedo. This tube will travel down the length of the boat to a bourdon tube (most likely mounted to the transom wall, you may not have one). From the bourdon tube, the hose continues to the transom and out the back to the pickup, which is nothing more than a rigid tube angled for water pickup. There are several spots along the tube where mold/mildew/debris can clog the system, but the most common are near the extremities of the tubing. More than likely, you have debris in the pickup. A good method to remove it is to use a small tool, like a drill bit, to reach in and pick it clean. On the instrument side, you can clean it in a similar fashion. I keep a drill bit on a cork in my tools to remove debris while on the water. You can blow into the hose, but this will not likely loosen the debris. Picking it clean works most of the time. If the hose is so bad it needs replacing, skidim.com carries the hose and it is very cheap. (Message edited by olSkoolTige on April 21, 2008)
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