Sooner or later, there comes a point in the life of every marine engine when a simple tune-up will no longer restore lost power. When that inevitable moment arrives, you're left with two basic choices: You can either endure the sluggish performance and diminished fuel economy of a tired engine, or you can re-power.  Re-powering refers to three different projects and three different levels of expense. In its simplest sense it means overhauling an engine. On a more ambitious level, it can refer to a complete rebuild; or, at the highest level, it means replacing the existing power plant with a factory-new engine. So, after deciding whether or not to re-power, you then have to decide how you're going to do it.