Alarm about cooling in lower rpm

[SuzukiPeter]

Having issues with my Suzuki DT-100 -90.

In neutral, about 2000 rpms, the motor runs without alarm.
When decreasing the rpms to about 1500 rpms the alarm starts. After the motor has been running for a while in neutral and gotten warmer then it warns first around 1000 rpm. So I cannot go completely down to idling without the alarm setting off.

It is only on the right side of the engine.

The red arrow in the attached picture points to the red light that turns on when the alarm goes off.

So I am guessing the issue is either:
1. Problem with the sensor on the right side
2. Problem with the thermostat on the right side
3. Something stuck in the water channels on the right side

Am I totally off? Suggestions?

43226790-F5BD-48CB-8946-F2F7DF2D982B.jpeg

ps I live in Sweden

[2014DF25ARS]

I had a similar experience with my Suzuki DF25A motor, which I wrote about two years ago in this forum. It would overheat at idle, but would run all day without problems at higher RPM. In my case, the tip was broken on one of the impeller blades of the water pump. I replaced the impeller and have not seen any cooling problem since. The water pump spins at a speed proportional to the engine RPM, so if the water pump is not working at full efficiency, then you do not get the sufficient water circulation at low RPM. I don't know what the "left-hand light" vs the "right-hand light" means on your gauge. I have never heard of an engine that had separate water cooling for the two sides of the engine. But I don't have experience with many different engines. On my engine, there are two cooling failure modes: one failure is when the temperature is simply too high. Another failure is when the temperature increases at an unexpected rate. Maybe this is what your second light is for? Or it appears that maybe the left light indicates that the motor is being rev-limited due to a cooling issue.