Again, it sounds like this engine is acting exactly as it was designed to. If not equipped with a heat exchanger, it will only discharge a small amount of water when cold. Absolutely normal and as intended. My does the same thing, just a dribble at cold idle. As the engine warms up the flow increases, it will only discharge the amount that passes through the thermostat. It's a 140 deg t-stat and there's little flow until it reaches 140. Mine never goes above 170 no matter the load, this is still below normal temp for a fresh water cooled engine. If it's not overheating, there's nothing wrong with it. OP didn't say what the running temp was.
The owner's manual is attached, page 35 is the cooling system. Follow the diagram and visualize what's happening there and it will be clear. Water comes in the intake to the pump, through the block, then to the t-stat. If t-stat is closed only a tiny amount gets discharged. The rest goes to the tee at the intake, the same amount that was discharge gets pulled in, and the water flows through the engine again. It's very effective, and will even heat a water heater connected between the t-stat and the intake tee.