I gave myself a hyrolock this past fall. The primary problem that started off the whole mess was water in the fuel.
In literally the last motor to the fuel dock to pump out, just before haulout, the engine stopped .... of course, right in the middle of the fairway with rocks of one side and boats on the other. After getting ourselves to a dock, and checking things, I determined that water was my problem. So, I drained the filter, and pumped my primer bulb until only clear fuel came out. After turning over a bunch, it still didn't start, so I assumed I might have got some air into the system, so I started the bleed process. Just as I was finishing the bleeding process, and had finished turning over the engine to bleed the injectors, and was turning over the engine to get it started, when it felt like it was just about to kick over as fire up, it stopped abruptly. That's when I realized that I forgot to close the intake seacock!!! I wasn't 100% sure there was water in the cylinders, but wasn't going to take the chance and the way it thudded to a stop was not normal.
To clear the water, I closed the intake seacock, then removed the exhaust from the input (bottom) of the water lift, and let it flow into the bilge under the engine. It happens that the layout of my boat make this manageable. I then opened the decompression valves, and then turned over the engine until no more water came out of the exhaust hose (a few cups of water came out during engine turnover). A quick touch of the starter button with the decompression levers closed and the engine turned over normally. Whew! Reconnected the exhaust, and it fired up immediately.
The process of trying to start with water in the fuel, then air in the fuel, then the bleeding process eventually filled up the muffler!
I have a speedseal cover, with the Teflon spacers, on my water pump, so I wasn't too worried about wrecking the impeller. Upon winterizing inspection, the impeller was fine.
Cheers
Chris