Honda Outboards BF40A/BF50A Service Manual, Page 227Get this manual
HONDABF35A45A Manual operation
The manual valve opens when it is turned counterclockwise, forming the manual passage to allow an easy manual tilt up or tilt down of the outboard motorWhen the manual valve is tightened fully clockwise while tilting updown the outboard motor, the manual passage closes and the outboard motor locks in the position