I have a 1986 20 hp Mercury. I just dropped the lower unit and swapped out the water pump impeller, the housing O ring, and the nylon seals that sit on top and bottom of the impeller. Before this the water stream was weak at best but there was water running through it. Since replacing these parts I can't get it to pump water at all. I've pulled it back down and double checked that the shaft key is installed properly, the O ring was set properly and that the connection to the tube that feeds the top end appear to be good. I've hooked it up to the garden hose with muffs and nothing. I also took my compressor and blew air from the top end to see if I had anything blocking the tube but it appears to be clear. Anyone have any suggestions on what I should be looking for next?