I lost water pressure on my starboard motor. Thought oh well, just an impeller. Tore into pump impeller good. back flushed everthing is fine, even flushing back from sea strainer to lower pickups in the outdrive's lower is fine. Problem: when I reverse flow (normal flow direction) to flush water from lower up to seapump i have a blockage. Do you think there is debris in the lower acting as a check valve? Just drop the lower and check?

check hose at transom connection,i had one go bad and acted like a check valve.inner part of hose seperated,easy to remove,located on inner gimble .

+1

I would also remove the fitting at the transom and look at the hose in there, they collapse from corrosion around the housing.

Think I found the problem. When the drive is all the way down the "S" hose is in a bind and pinching. I seldom run with the drives all the way down, and it was rough this weekend, hence running so long with the drives tucked all the way down. I must have had this problem for a while and must have twisted the hose deforming it's shape when installing the inserts. May go and get a new hose since I compromised the hose's bends. Will post up if this solves my problem.