i have a 200 hp. mariner that is not pumping any water starts runs fine fine but doesnt pump water, thought it might be the impeller so replaced it still nothing , then i removed the thermostats because they were all junk still no water ,the only thing i can think of could it be the pottet valve is no good and is that why im not getting water pupming through the motor, and if it is the poppet valve can i remove it and try it with out it in there or will that mess up the motor im at a loss dont know what eles to check please help if you can