I did my homework!
I also paid a certify Suzuki mecanic with no solution.
The alarm is still there.

New water pump, new thermostat, new temp sensor, flush with garden hose ...

The BF30 (2002) run OK at low et medium speed range, but after 3 to 4 minutes at WOT the alarm
goes on.

End of season. Will start with a new water pump next spring

Normand (Québec, Canada)