His service manual is right. There is a linkage from the throttle to the oil pump that varies the mix based on throttle. The merc oiling system is pretty good when properly maintained I wouldn't just go pulling it unless the drive gear on the crank goes bad or something. We do need to know which buzzer went off though. Solid beep is either overheat or lack of motion at the oil pump sensor either of which means shut it down NOW. 4 rapid beeps that repeat every couple minutes is the water sensor and rapid single beeps is the sensor in the lid on the small oil tank on the motor indicating low oil level. The latter is commonly caused by a loose cap on the reservoir inside the boat, or a pinched oil or air hose.