What is the model number of a Yamaha waverunner with the engine serial number 503820?

To determine the model number of a Yamaha Waverunner with the engine serial number 503820, you would typically need to refer to Yamaha's database or service manual, as engine serial numbers can correspond to specific models based on production year and specifications. However, without direct access to Yamaha's records, I cannot provide the exact model number associated with that engine serial number. It's best to consult a Yamaha dealer or check the manufacturer’s documentation for precise information.