Sometimes when I try to tilt up my motor (Mercury 40hp about 1980), it won't tilt because the "ratchet" that the tilt lock pin goes through has moved into a locked position. I have 2 questions: 1. What causes the ratchet to lock? 2. How to unlock it except by removing the tilt lock pin and unlocking the ratchet by hand? p.s. I am new to outboards, so I won't be surprised if this message is not crystal clear. Thanks.