Re: Evinrude 4425

[jasonh]

Several things come to mind.. The pump plate and deflector plate need to be in place as pictured in parts diagram Frank included. On the deflector, there is a stamped fluted center which can have a tendency to get misshapen or even busted or hogged out, its very thin metal… This seals with bottom lip of top impeller. Make sure the plate is present and still spot welded in deflector.Its also important that the impellers be installed with correct side up. The impellers may have the word UP embossed on them if not yet worn off to ensure this. The lips at the center of the impellers should not be torn or worn and should be facing down.. Basically make sure the curve in the vanes match the picture Frank posted. The other thing is the welch plug mentioned previously… There is a cavity that it cover to make a small opening in leg for water to travel up. The welch plug needs to be in place to maintain force. You can remove it to clean the above passage as needed but need to reinstall welch plug.

Here is my interruption of how it works (hope it translates well 😕 ):
Each impeller draws water from the center then throws it (centrifugal force) to the outer edges. The deflector is designed with a plate spot welded to it that has small gaps at the outer edge inside the top plate. The water thrown outwards from the bottom impeller (stage 1) feeds into those passages then into the center of top impeller (stage 2). The top impeller than again draws then throws the water to the outer edges (centrifugal force). The passage behind the welch plug is the path of least resistance and water travels up leg to powerhead. There is a balance of force and flow. Think of what happens when you put your thumb over the opening of a hose. The pressure for stream increases. Leave hose unobstructed and the volume increases but pressure decreases. That is why its important these passages be as they were designed in size and clearance as well as unobstructed. If you take the welch plug out, the center of defector gets misshapen or hogged out, or bottom plate is missing (turns bottom into a huge open hole) you change how the centrifugal forces are at work. If you have an obstruction, water just wont flow.