1963 75 HP Speedifour water intake

[SpeedifourButch]

1963 Evinrude 75 HP Speedifour<br /><br />The above motor is completely rebuilt with about 12 hours on it. Water pump works fine. Thermostat is new and works fine. Cooling passages are not clogged. Since I have not yet found a set of flush muffs, I fashioned a device to fit the hole under the cavitation plate. The motor was hot enough for the thermostat to already be open as I had just pulled it from the water and it was warmed up. I hooked up my gizmo and started the motor with the water pressure on. No water pumped out. I ran it for a minute or two and still no water. I shut it off and put it in the barrel I have been using to flush it out. Once the water reached the hole under the cavitation plate I started the motor again and still no water.<br /><br />It was not until the water reached the small slot , (about 3/8" x 1 1/2") on the port side on the motor that she started pumping water. Thinking the thermostat had closed by the time I filled up the barrel, I emptied the water level until it once again was at the level of the hole under the cavitation plate. Started her and she did not pump.<br /><br />Sorry for the long explaination, but I'm trying not to waste everyone's time with numerous replys asking the specifics.<br /><br />My question is, do both of these openings, (sub-cavitation plate and port side of engine just above cavitation plate), need to have water fed to them in order for the pump to pump? And, if I can supply water to the small hole above the cavitation plate without water to the lower hole, will that supply the motor with water?<br /><br />Also, does anyone know of a way to "tap" into the block, or where I would do so in order to install a water pressure and/or temp gauge?<br />Any and ALL advice appreciated,<br />SpeedifourButch