I applaud your caution, these engines actually do have a complicated water pump and cooling system. Running them in a barrel/bucket can be deceiving, they are very sensitive when it comes to the water pump. You might try launching the boat and running it that way, if you have a boat that is. Keep in mind, it is perfectly normal to seen nothing coming out of the cooling/exhaust relief hole until the engine warms up and the thermostat opens, even then you will only see a fine spray for a minute or so while the thermostat is open, very confusing.
Don’t get me wrong, it is always a good idea to service the water pump, but it is tricky on this style engine. Wish I lived nearby, but don’t, sorry.
